lustre2 input plugin not customizable due to TOML parsing issue

[shawnahall71]

As requested by @danielnelson in #5771.

Relevant telegraf.conf:

# Read metrics from local Lustre service on OST, MDS
[[inputs.lustre2]]
  # An array of /proc globs to search for Lustre stats
  # If not specified, the default will work on Lustre 2.5.x
  #
   ost_procfiles = [
     "/proc/fs/lustre/obdfilter/*/stats",
     "/proc/fs/lustre/osd-ldiskfs/*/stats",
   #  "/proc/fs/lustre/obdfilter/*/job_stats",
   ]
   mds_procfiles = [
     "/proc/fs/lustre/mdt/*/md_stats",
   #  "/proc/fs/lustre/mdt/*/job_stats",
   ]

System info:

Telegraf 1.11.2 on CentOS 7.4

Steps to reproduce:

Use the above Telegraf config on different versions of Telegraf.

Expected behavior:

When I use telegraf 1.10.4, it works as expected:

# telegraf -config /etc/telegraf/telegraf.conf.test -test                                                                                                                                                                            
2019-07-10T13:01:29Z I! Starting Telegraf 1.10.4
> cpu,cpu=cpu0,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.00000004470348,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=1.999999996041879,usage_user=0 1562763690000000000
> cpu,cpu=cpu1,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.0392157292421,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=1.9607843164109648,usage_user=0 1562763690000000000
> cpu,cpu=cpu2,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu3,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.0392157292421,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=1.9607843164109648,usage_user=0 1562763690000000000
> cpu,cpu=cpu4,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.0392157292421,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=1.9607843164109648,usage_user=0 1562763690000000000
> cpu,cpu=cpu5,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=94.1176471662425,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=1.9607843214322427,usage_steal=0,usage_system=1.9607843178655968,usage_user=1.9607843214322427 1562763690000000000
> cpu,cpu=cpu6,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=96.0784314584842,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=1.9607843164109648,usage_user=1.9607843149843065 1562763690000000000
> cpu,cpu=cpu7,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu8,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu9,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu10,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu11,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.0000000372529,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=2.0000000034924597,usage_user=0 1562763690000000000
> cpu,cpu=cpu12,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu13,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu14,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.0392157292421,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=1.9607843164109648,usage_user=0 1562763690000000000
> cpu,cpu=cpu15,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=100,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0,usage_user=0 1562763690000000000
> cpu,cpu=cpu-total,host=hpclbo00 usage_guest=0,usage_guest_nice=0,usage_idle=98.87359194657252,usage_iowait=0,usage_irq=0,usage_nice=0,usage_softirq=0,usage_steal=0,usage_system=0.876095115754831,usage_user=0.2503128910482447 1562763690000000000
> mem,host=hpclbo00 active=62780149760i,available=121160527872i,available_percent=89.99860804344,buffered=312258560i,cached=125641707520i,commit_limit=84458754048i,committed_as=5131505664i,dirty=217088i,free=1769193472i,high_free=0i,high_total=0i,huge_page_size=2097152i,huge_pages_free=0i,huge_pages_total=0i,inactive=61960777728i,low_free=0i,low_total=0i,mapped=366833664i,page_tables=8921088i,shared=2399195136i,slab=3043733504i,swap_cached=4153344i,swap_free=16910118912i,swap_total=17146310656i,total=134624890880i,used=6901731328i,used_percent=5.126638382312203,vmalloc_chunk=35113034797056i,vmalloc_total=35184372087808i,vmalloc_used=2496950272i,wired=0i,write_back=0i,write_back_tmp=0i 1562763690000000000
> swap,host=hpclbo00 free=16910118912i,total=17146310656i,used=236191744i,used_percent=1.3775076676179872 1562763690000000000
> swap,host=hpclbo00 in=5046272i,out=234377216i 1562763690000000000
> system,host=hpclbo00 load1=0.64,load15=1.4,load5=1.08,n_cpus=16i,n_users=1i 1562763690000000000
> system,host=hpclbo00 uptime=9459500i 1562763690000000000
> system,host=hpclbo00 uptime_format="109 days, 11:38" 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0002 cache_access=123120213i,cache_hit=25947190i,cache_miss=97559888i,read_bytes=134929587335168i,read_calls=123616552i,write_bytes=89420750561807i,write_calls=24129027i 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0003 cache_access=118437662i,cache_hit=14497478i,cache_miss=104385527i,read_bytes=131436306927616i,read_calls=119764309i,write_bytes=90039578607203i,write_calls=23623436i 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0004 cache_access=115649287i,cache_hit=23159646i,cache_miss=92797258i,read_bytes=125015997210624i,read_calls=116213700i,write_bytes=77198517324719i,write_calls=20875544i 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0005 cache_access=114102041i,cache_hit=23505459i,cache_miss=91084552i,read_bytes=121714593878016i,read_calls=115034217i,write_bytes=82191539574894i,write_calls=21949600i 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0006 cache_access=119626413i,cache_hit=19527210i,cache_miss=100433697i,read_bytes=136805938708480i,read_calls=120691366i,write_bytes=87532199845233i,write_calls=23370151i 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0000 cache_access=138117149i,cache_hit=40481815i,cache_miss=97947712i,read_bytes=149839448764416i,read_calls=138522648i,write_bytes=86155537532047i,write_calls=22975409i 1562763690000000000
> lustre2,host=hpclbo00,name=lustreb-OST0001 cache_access=125596425i,cache_hit=25840974i,cache_miss=100043275i,read_bytes=135576462835712i,read_calls=126334658i,write_bytes=80814717739044i,write_calls=21773289i 1562763690000000000

Actual behavior:

When I use this config with Telegraf 1.11.2, uncommenting the default inputs.lustre2 configuration (even without commenting out job_stats) produces an error:

# telegraf -config /etc/telegraf/telegraf.conf.test -test 
2019-07-10T12:52:08Z I! Starting Telegraf 1.11.2
2019-07-10T12:52:08Z E! [telegraf] Error running agent: Error parsing /etc/telegraf/telegraf.conf.test, line 3009: field corresponding to `Ost_procfiles' is not defined in lustre2.Lustre2