Make the user able to specify full path for HAproxy stats

[tgermain]

Do no try to guess HAproxy stats url, just add ";csv" at the end of the
url if not present.

It inspired by #1034 (comment) and should fix #1019 .

Signed-off-by: tgermain timothee.germain@corp.ovh.com

[phemmer]

The only effective change this makes is that it removes the trailing /.

[[inputs.haproxy]]
    servers = ["http://localhost:1234/foo/bar"]

master (300d9ad):

GET /foo/bar/;csv HTTP/1.1
Host: localhost:1234
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip

this PR (ff82b1c)

GET /foo/bar;csv HTTP/1.1
Host: localhost:1234
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip

[tgermain]

Not only, it also take into account the query string part of the url which was dropped before.

Configuration :

[[inputs.haproxy]]
  servers = ["http://localhost:5656/haproxy?stats"]

Master branch:

127.0.0.1 - - [18/Jul/2016 07:52:10] "GET /haproxy/;csv HTTP/1.1" 404 -

This PR:

127.0.0.1 - - [18/Jul/2016 08:30:40] "GET /haproxy?stats;csv HTTP/1.1" 404 -

Since the default uri of HAproxy stats is /haproxy?stats I think that making the nominal case works is important.

For the trailing / I can add it, both /haproxy?stats;csv and /haproxy?stats/;csv are valid.

[sparrc]

@tgermain the latest change appears to have created a test failure, and you'll also need to rebase your change before I can merge.

[tgermain]

My bad for the test failure, tests are passing now.
The PR is also rebased.