Shutdown the cluster properly on Windows

Windows differs from Unix/linux with respect to how processes
and their relationship works. By using .kill() resulted in
a lot of the processes erl starts to be running (and a
callstack being printed from Python that signal.SIGKILL
isn't supported..

Change-Id: I7d3f13faa4ab722ecde7335ac178b7a911f6f7c7
Reviewed-on: http://review.couchbase.org/40565
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>