Fix graceful recovery after environment shutdown

[micahyoung]

• Support bosh create-env after director is hard-shutdown
• Support bosh create-env when VMX files have been deleted
• Support bosh deploy for existing deployment after VMs are shutdown
• Support bosh recreate for existing deployment after VMs are shutdown
• Support bosh deploy when VMX files have been deleted

[micahyoung]

I made some commits to handle simple scenarios. At this point, I think I just need to document how to manually work around each of these scenarios.