Remove use of "quota_tenant_usages" in Volumes page

Replace it instead with a direct call to the Cinder limits. The
generic usage quotas method performs some operations that can be
costly when there is a large number of volumes.

Change-Id: Ib5601d34a1854f4b190b3bc106504f384561fc30
Partial-Bug: #1334608
Merge "Remove use of "quota_tenant_usages" in Volumes page"