CBQE:0 Add xdcr trace logging for system tests

Change-Id: Ie7cb451314a0863b858ee6ef3f59705828ccbd8d
Reviewed-on: http://review.couchbase.org/39362
Reviewed-by: Aruna Piravi <aruna@couchbase.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>