Bootstrapping an existing environment with no .jenv file no longer destr...

https://bugs.launchpad.net/juju-core/+bug/1336843

Tests are not yet written as there will be much overlap with another PR which is yet to land. I will not merge this without tests.
Ah, right. You could declare info before the if/else chain, but I think this is fine now I see why you are doing it.