Run processes in new pgroup

[davishmcclurg]

Some processes are getting orphaned when running Foreman with JRuby. Creating a new pgroup allows them all to be killed together.

I believe the issue is related to how JRuby handles Dir.chdir by creating a shell process: sh -c 'cd /chdir/target; ${command}'. That causes a second process to be created that won't get cleaned up by killing the parent.

[baelter]

This PR is needed for rerun to work with foreman on Ubuntu.

[davishmcclurg]

This PR is needed for rerun to work with foreman on Ubuntu.

I think there's a new version here: https://github.com/ddollar/foreman/pull/780

[baelter]

@davishmcclurg Yes, that was actually the branch I tested with.

[dentarg]

I forked foreman and merged #780 (this PR but rebased) and released the fork as overman: https://github.com/spinels/overman, https://rubygems.org/gems/overman, #780 (comment)