gluster: add task support

gluster volume operations like rebalance, replace-brick, remove-brick
are async operations which needs to be tracked as async tasks in
oVirt. This is done by introducing below new verbs.

New verb:
* glusterTasksList
    - return value structure:
        {TASKID: {
                  "volume": VOLUMENAME,
                  "status": TaskStatus,
                  "type": TaskType,
	          "bricks": [BRICK1,..],
		  "data": SUMMARY
                  }, ...}

Change-Id: I154df353bc6f23001d7bf61b8f5345abd2019cb6
Signed-off-by: Bala.FA <barumuga@redhat.com>
Signed-off-by: Timothy Asir <tjeyasin@redhat.com>
Signed-off-by: Aravinda VK <avishwan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/10200
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>