Cinder extension to add used resources in absolute limits

* totalVolumesUsed
* totalGigabytesUsed

DocImpact
Implements: blueprint cinder-used-resources-in-absolute-limits
Change-Id: I525a61043ce2f906c424738ab361ee7396f072b5
(cherry picked from commit 8aa8ebc0a0d0f459e9293f9ff5a5f8358fd01b9a)