CBQE-0: added function to modify remote clusters in xdcrbase class

Change-Id: Id66db0b1e67727d5d947e6376d104bebddf835de
Reviewed-on: http://review.couchbase.org/32304
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>