Fix for #14 thanks to @chino and fixing an issue with destroying VMs

This PR has 2 changes:
- https://gist.github.com/chino/603f23b21d67c0541f4f/ - Thanks @chino!
- Destroying VMs was broken if other VMs were powered off. On destroying VM 1, the plugin would attempt to ssh / sudo into each other VM to update their hosts file. This would result in the plugin failing to ssh into the other powered off VMs, and leave VM 1 in a powered off state (and not destroyed)