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.
Related to https://bugs.launchpad.net/juju-core/+bug/1340893
It returns an error if one occurred... if there are no errors? This sentence is a bit confusing.