Fix vcloud-director NatServce opening DNAT

- Ensure all services are uploaded when editing, so don’t overwrite 
  existing config.
- openPortForwarding to return what was just created, throwing if failed 
  and warning if duplicates.
- Allow logging level to be configurable.
- Adds enableNatService (because was broken for customer by being
  disabled, so useful to have this utility).
- Adds to VcloudDirectorSubnetTierLiveTest tests for doing it
  by network_name and by network_id