webadmin : remove-brick status error handling

Errors like,
1. If some/all the hosts forming a distribute volume with atleast 2 bricks are
   down, and if rebalance status is triggered on such a volume, approprite
   error message is displayed.
2. If any n/w related or any other exceptions are thrown,they are also
   handled properly.
And hence the popup doesn't hang anymore.

Change-Id: I57bb82ebc0318266f32262c6f9bb245e26f2ddd1
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1027675
Signed-off-by: Anmol Babu <anbabu@redhat.com>