gluster: Update volumes by id instead of name

Modifying the logic to compare fetched volumes with existing volumes
to use volume ids instead of name. This handles the rare scenario
where someone deletes a volume and creates a new one with exactly
same name from the gluster CLI, in quick succession.

Change-Id: If9053da4294b7c5aa762645737a2effccd5a9c4d
Bug-Url: https://bugzilla.redhat.com/888144
Signed-off-by: Shireesh Anjal <sanjal@redhat.com>