Fix VMwareVCdriver reporting incorrect stats

fix bug #1180779

VMware nova compute drivers VMwareESXDriver and VMwareVCDriver
currently report stats for the column local_gb in MB instead of in GB
The fix would be to modify vmwareapi/host.py to ensure the values
reported for disk space are calculated in GB instead of MB.
Fix is done by further dividing the existing MB value by 1024 to
convert to GB.
The unit tests to check for capacity and freespace have been modified
to check for GB.

Change-Id: I0610047ee2bddefe0ccb46568c0f48de4c0941af
Merge "Fix VMwareVCdriver reporting incorrect stats" into stable/grizzly