Bootstrap no longer cleans up if it can't tell whether an environment is bootstrapped or not.

Added a test to simulate an instance in which this might occur. Tested locally; some tests were failing, but they looked innocuous and related to connecting to mongo, not these changes.
Very nitpicky, I know, but "x != err" is pretty unusual for Go code in general, and I don't recall coming across it at all in Juju. I'd prefer if you stuck to the project's conventions, barring strong arguments for change.