CBQE:0 Fix minor error in enabling xdcr trace logging in sys tests

Change-Id:  I2c472be770e5341eaf155b5e80b1f791c7494a32
Reviewed-on: http://review.couchbase.org/39892
Reviewed-by: Aruna Piravi <aruna@couchbase.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>