Moved openstack env variables out of snapcraft.yaml, and into a
"microtack.rc".
Made openstack-wrapper, which auto sources microstack.rc.
Key off of revised snap.openstack, which supports snapctl config
values in templates. Moved a lot of the overlay into
snap-overlay/templates, and added config values to them. Also writes
templates just once, when you run snap-openstack setup.
Giving the snapcraft.yaml a base property helps tremendously with the
efficiency of the build process, and I believe that it puts us in a
better position to reliably support non Ubuntu distros going forward.
This also bases us on long supported bionic libraries, and gives us a
nice place to work from as we add Python 3 and Stein support, as well
as general polish and fixes.