gluster: Disable Rebalance/Remove Brick when one or more bricks are down

  When one or more bricks are down in a distributed volume or one complete set
of replica pairs are down in a distribute-replicate volume, Rebalance/Remove Brick operation
should not enabled as it will anyway fail in gluster side.

Change-Id: Ib66fe531dfea6099a449fcae8c4370711ae3dd8b
Signed-off-by: Ramesh Nachimuthu <rnachimu@redhat.com>