As 284, part 2 - check for server on nova error

This part actually does the create server retries after checking to make sure no server was created.  This is based on https://github.com/rackerlabs/otter/pull/647
I think it may be useful to destructure that. Also, whence the unquote? Is that so that we wouldn't be testing any particular quoting behavior, as long as it's doing some correct quoting?