Auto 339 delete server if group deleted (waiting on #275)

This deletes servers that are finishing building if `modify_state` fails to pull up a state for the group, which indicates that the group has been deleted.

This depends up on the changes in #275 - these are the only changes on top of that PR:  https://github.com/rackerlabs/otter/compare/controller-job-refactor...auto-339-delete-server-if-group-deleted