Create the glance.store repo

The patch adds a new glance.store repository that will contain all the
code for the new glance.store library. This work is part of the
blueprint create-store-package that aims to pull the stores code out of
glance.

Change-Id: Iea3b5c2e82e87868bdf9cae6a32b5895b792e3d8
Merge "Create the glance.store repo"