As 284, part 1 - find a created server on Nova (ready for review)

This change is bigger than I thought, so I am trying to break it up into bits.  This part just provides the functionality to check Nova for an exact server that matches a given server config, created around a certain time.

Question for the next part - should we wait at all after getting a 500 or 401 response back from Nova from creating a server, before checking Nova to see if a server was created? 
This line will work, but the formatting will be a bit weird. The first argument to log.err in kinda-sorta supposed to be a failure object (or None, in which case the current exception returned from sys.exc_info() will be used), and the second argument is supposed to be a textual explanation of the error.

Since there's no exception in this case, I would suggest just using log.msg and passing some unique keyword arguments so it's filterable.