CBQE-0: minor improvements in membase_upgrade_win

Change-Id: Iee52720db19f9f791c9b716e47ff419398d313e6
Reviewed-on: http://review.couchbase.org/26828
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>