Rename glance.store into glance_store

glance.store relied on python namespaces. Since setuptools doesn't
handle python namespaces correctly for py27 - nor it will - we've
decided to rename the package into glance_store to avoid the problem and
any workaround altogether.

Mailing list discussion:
http://lists.openstack.org/pipermail/openstack-dev/2014-August/044194.html

Change-Id: Iedfe8d4d450a8ab9edc2de62b666c1b7a0f3171e
Merge "Rename glance.store into glance_store"