Added topic for configuring datastore backend for Glance

I added a new file describing how to configure datastore backends
for Glance in vCenter and the glance conf file. Also added an
include so the new topic appears as a child topic.

Change-Id: I9cb90ff4b4b0689dc9e85d40681044dfeb5029d1
Closes-Bug: #1311814
Merge "Added topic for configuring datastore backend for Glance"