Does not handle start_failed instance status

They have the full list of possible statuses here:
http://docs.aws.amazon.com/cli/latest/reference/opsworks/describe-instances.html

- `booting`
- `connection_lost`
- `online`
- `pending`
- `rebooting`
- `requested`
- `running_setup`
- `setup_failed`
- `shutting_down`
- `start_failed`
- `stop_failed`
- `stopped`
- `stopping`
- `terminated`
- `terminating`