gluster: Using XML output for rebalance/remove-brick status verbs

Modified rebalance/remove-brick status output to consume XML
output provided by gluster cli command.

Modified verbs(As below verbs are not consumed by engine/RHS-C yet,
its OK to differ in compatibility issue now)
glusterVolumeRebalanceStatus
glusterVolumeRemoveBrickStatus

Output:
    {'summary': {
        'filesScanned': INT,
        'filesMoved': INT,
        'filesFailed': INT,
        'filesSkipped': INT,
        'totalSizeMoved': INT,
        'status': STRING
    },
    'hosts': [{
        'name': STRING,
        'filesScanned': INT,
        'filesMoved': INT,
        'filesFailed': INT,
        'filesSkipped': INT,
        'totalSizeMoved': INT,
        'status': STRING
    }]}

Change-Id: I7d277f267cf64d8af419d07367c33dc065f86a9b
Signed-off-by: Bala.FA <barumuga@redhat.com>
Signed-off-by: Aravinda VK <avishwan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/18358
Reviewed-by: Timothy Asir <tjeyasin@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>