Bug 1392795 - [yamllint] Group paths to lint by their closest config and run...

Bug 1392795 - [yamllint] Group paths to lint by their closest config and run each config group separately, r=dustin

This makes configuration files for yamllint work a bit better. It's still not perfect, but it's an improvement
on the current situation.

MozReview-Commit-ID: IKxgQm1a7bP

--HG--
extra : rebase_source : 051fafe21337f0557ee39ec71c90e74fd61d3da7