CBQE-0: add doc string for remaining functions on xdcrnewbasetests.py

Change-Id: I354a54abd6c8036b1e52210fb17595dcb135884c
Reviewed-on: http://review.couchbase.org/43464
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>