Better status information when a relation hook fails

The first commit makes a  bunch of changes which take advantage of new data now available in the FullStatus API response to show the remote endpoint details when a relation hook fails. This addresses LP #1194481.

The second commit refactors the status formatting code to make some of the changes made in the previous revision somewhat cleaner.
I'm pretty sure this is an "old server that" ...
Given that where you are right now is the client code, right?