This has the disadvantage that we can only use the current tree to
collect evidence of overlap -- this means that it's possible for file
addition or deletion to force a CODEOWNERS update.

HOWEVER, it has the advantage that it's correct and propagates ownership
in the way that we want (alleviating murgatroid@ from having to approve
every additional file in the repository)

-) Paths should all be absolute to /
-) Computing the intersection of two globs should happen with the
full path in there, not just the directory's glob.

This reverts commit 3d04e025.

Created test driver to run matrix test against different docker images in GCR and generate a Junit like test result file.