Verify and Create Tags from Release File

Updates the releases verify and merge jobs to check release files for
the following:

 - commits exist
 - commits are on stable-branch

If both of these criteria are met and the patch is merged, the repos
will be tagged at the specified commits and pushed.

If a repo has already been tagged but not on stable-branch the job will
not exit, but will warn that the commit doesn't exist on the correct
branch. This is because tags should never be removed.

This adds an additional script 'repos.py' that provides an quick
interface for pulling out information from release files, along with the
script 'release-status.sh' for checking the status of tags.

NOTE: The branch creation script has been disabled until it can be reworked.

Change-Id: I498bc74f20aa50d2bd321771f20a77905b246399
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>