Add the volume and snapshot gigabytes together.

The quota sync functions were not working correctly for both
snapshots and volumes regarding gigabytes. Each would report
their own count as the total gigabytes.

Now the gigabytes sync is separate from the volume and snapshot
count syncs.

Fixes bug #1160004

Change-Id: Ib1200813acb6055412b3f7f6b63fa9ba2b8fa3be
(cherry picked from commit 1fde5a4fbc73a31453f0fe288a0b4a929d7f3026)