JCLOUDS-317: Add missing states to Nova v2 Server

- Remove state: STOPPED
- Add states:   MIGRATING, SHUTOFF, RESCUE, SOFT_DELETED,
                SHELVED, SHELVED_OFFLOADED

- Related blocker issue: https://issues.apache.org/jira/browse/JCLOUDS-317
- It would very nice if, in case of being merged, the pull request could be backported to the 1.7.x branch.