gluster: Query to get gluster bricks by task id

Added a query to get gluster volume bricks by task id. This enables
listing the set of bricks participating in a single task of
remove-bricks action.

Change-Id: I91c5074f29f1913a1b39f00de277c74aacf8bf46
Bug-Url: https://bugzilla.redhat.com/1040686
Signed-off-by: Shubhendu Tripathi <shtripat@redhat.com>