CBQE-0: remove shutdown step from upgradeXDCR tests

Change-Id: Ibef1de7b34b94d732c64f8c57c2ffc321097ff22
Reviewed-on: http://review.couchbase.org/36890
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>