Prompt User for Bucket Destruction at Cluster Destruction

[dylanbannon]

Is your feature request related to a problem? Please describe.
We have excessive numbers of buckets building up in our Gcloud account, due to users (like me) naively using the default configuration settings, which will create a new bucket but won't delete it ever.

Describe the solution you'd like
There are good reasons not to delete the cluster's bucket by default, but I'd like to see a prompt come up after a user selects the Destroy menu option to ask whether the user wants to delete the "associated bucket ____, too". I feel like this would be useful only if the bucket were created at the same time as the cluster. (i.e., we shouldn't prompt someone to delete one of our important buckets, like deepcell-output, ever.)