CBQE-0: cluster.shutdown with force=True

still see runs where tests hang after failures in setup/tearDown

Change-Id: I06ea7d85399f8f762e756b2f18fd534c4e1860f3
Reviewed-on: http://review.couchbase.org/33878
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>