CBQE-0: move function from biXdcr.py to xdcrbasetests.py to reuse it

Change-Id: I82639673f01d9dd0e8e6ce2669eeabeea932d95b
Reviewed-on: http://review.couchbase.org/34465
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>