Support to configure VMware Datastore Store as glance backend store

Update the glance-api.conf and glance-cache.conf template files to
support configure VMware datastore attributes.

Implements: blueprint vmwareapi-support
Change-Id: If9f6dadf43a52d0a673043ea23edaf653f452a11
Merge "Support to configure VMware Datastore Store as glance backend store"