Fix race in test.
Merge pull request #631 from howbazaar/fix-envuser-race

Fix race in test.
Add bootstrap flag to allow failed bootstraps to keep the environment
Better warning message
Better warning message
Merge pull request #634 from wallyworld/keep-env-flag

Add bootstrap flag to allow failed bootstraps to keep the environment

Fixes: https://bugs.launchpad.net/juju-core/+bug/1362923

bootstrap now has a keep-broken flag which tells it not to cleanup after a failed bootstrap