Code review comment for lp:~hazmat/pyjuju/sane-relation-ids

*** Submitted:

Fix relation-ids cache coherency for hooks.

Relation-ids was answering questions about relations
directly from state, whilst other pieces of relation-*
cli was using a hook execution cache. This led to
odd races where a hook would query relation-ids
and then attempt to use relation-list/etc against
that relation resulting in a relation not found error.

This branch also does a drive by to improve the error
reporting for relation not found to include the relation
id where applicable.

R=bcsaller
CC=
https://codereview.appspot.com/7241062

https://codereview.appspot.com/7241062/