Code review comment for lp:~wallyworld/goose/rate-limit-retry-tests

*** Submitted:

Rewrite rate limit retry tests

This branch uses the new service double control hooks introduced in the
previous branch to rewrite the tests which check that rate limit
exceeded retries are handled properly.
The kludge used previously to induce a retry error has been removed, and
now an additional test can also be easily added to check the behaviour
if too many rate limit retry responses are received.

So that the tests run fast, I've allowed for the Retry-After header
value to be a float (even though a real instance only assigns an int).
This means the tests can specify a really
short retry time (I used 1ms).

I've also re-added a rate limit retry test for use with the live
instance, but improved it so that it exists as soon as the first rate
limit exceeded response is received.

R=jameinel
CC=
https://codereview.appspot.com/7200049

https://codereview.appspot.com/7200049/