Test issues with cluster and opening new buckets

When you are in a ClusterTestCase (or one derived from that), the self.cluster works fine, except if you try to open another bucket. If you do, cluster.bucket("bucket_name") always raises an AuthenticationException.

Perhaps there are a few things going on here - with regards to v2 style bucket auth and so on. However for the purposes of this ticket, maybe we can just get this to work within the tests? Perhaps all that is necessary is converting to a different Authenticator (maybe PasswordAuthenticator)? I recall trying that, running into other issues, and moving on as I had other things to do. But this is worth fixing - PYCBC-831 for instance would be great to actually test by opening up a few buckets – also diagnostics would benefit from this extra testing, etc...