Convert aggregates testing to use httpretty

This is the first in the series and so contains some setup classes. In
general the original data will not be able to be removed from fakes
until the very end because testing shell depends on a lot of it.

Change-Id: I499fe968923b9452f60c1b2ca50d5749e89827de
blueprint: httpretty-testing
Merge "Convert aggregates testing to use httpretty"