NCBC-243: Fail when requested nodes are greater than online nodes

Change-Id: Iab02a387d60b15c640279efaa2fff4257f66ceef
Reviewed-on: http://review.couchbase.org/25410
Reviewed-by: Saakshi Manocha <saakshi.manocha@globallogic.com>
Tested-by: Saakshi Manocha <saakshi.manocha@globallogic.com>