Support restarting already running jobs

[tadeu]

Currently, if we tell jobs to run using !build and they are already building, Jenkins will only add new builds to a "queue", and will wait until current builds finish to start building them again. By the default it could cance current builds, so that they are immediately restarted. If the old behavior is useful, it could be a different command (or via a flag), like !build 0 1 --queue or something like that.

[nicoddemus]

This is a bit dangerous because cancelling the jobs at an arbitrary point might render the conda env unusable lately for example, so not sure this is a good thing to have.