JcloudsLocation: support port-forwarding

- Refactors methods for creation of users
- Adds JcloudsPortForwarderExtension
- Calls out to port-forwarder for port 22, if configured
Support JcloudsLocation.newSubLocation specifying sub-type
JcloudsLocation port-forwarding: incorporate review comments
Merge pull request #1082 from aledsage/feature/JcloudsLocation-for-portforwarding

JcloudsLocation for port-forwarding