restructure stackrc into groupings

in order to support installing from stable libraries we first need to
actually sort out all the categories our giant list of git repos fit
into. This will make it much easier to not lose one in the process.

Change-Id: I708c65428fdc7442e1661037f425e466048166d3
Merge branch 'master' of https://github.com/openstack-dev/devstack