gluster: Fixed deadlock in nested command execution

The CreateGlusterVolume command internally calls SetGlusterVolumeOption.
Both these try to acquire exclusive lock on the cluster, resulting in a
deadlock. To fix this, Modified GlusterCommandBase to acquire a lock on
the cluster only if it is not an internal execution.

Change-Id: Id080ad6ac3587ab9c3443cb83969783955dfb082
Signed-off-by: Shireesh Anjal <sanjal@redhat.com>