Tidy up tests/base.py
Tidy up tests/base.py

This is a general tidy up and squashed commit of 3 previous changes
to ease reviewing.

- Generalize event queue handling in tests

Store the event queue list in the base test class, so operation on the
queues can be delegated to separate method instead of operating on each
queue explicitly. Previously: I4c23143b4d49fa409fe378d1348bb6397b748cb9

- Don't pass fake_gerrit to FakeURLOpener

It's not used there whatsoever.
Previously: Ieefb09aaf60d4044c567b4d51fedf2068c3de1a6

- Pass upstream_root to fake gerrit explicitly
Previously: Ifb7d47caec430d0a209140e87ada98b8531c5d04

Co-Authored-By: Joshua Hesketh <c028c213ed5efcf30c3f4fc7361dbde0c893c5b7@nitrotech.org>
Change-Id: I4c23143b4d49fa409fe378d1348bb6397b748cb9

gooddata/zuul,gooddata/zuul,gooddata/zuul,gooddata/zuul,gooddata/zuul