restapi:Correct rsdl for add bricks

Add bricks command causes an exception in cli
when passed a collection of bricks.
Changed the rsdl to brick--COLLECTION
as per Michael's suggestion

Change-Id: I2a229faa90c8fcded33b53ab8801c4cb03094798
Bug-Url: https://bugzilla.redhat.com/923169
Signed-off-by: Sahina Bose <sabose@redhat.com>