CBQE-1961: fix tuq xdcr tests hunging

second cluster object was created - added a check to not to create second if there is already one existing

Change-Id: Ifc0d29316c9cea894b3d14e7e4ad2cc465555d7b
Reviewed-on: http://review.couchbase.org/34627
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>