Comment 2 for bug 1172418

Related review (to allow the mirror script to take a specific branch name on the command line):

https://review.openstack.org/28346

The impetus is, since the openstack/requirements project now has stable branches, the mirror script is taking three times as long to run. Changes to the repo are only going to land on a specific branch however, so long-term we won't want to update mirrors for all branches when triggered from a job in the post queue (only when triggered from a periodic job).

Once that merges, we can add the ability to create branch subdirectories of the current mirror. I'll ponder the layout a bit and throw some ideas in here.