some fixtures that "capture" no longer work with the removal of testtools

[cdent]

In #279 testtools was removed.

Fixtures in the openstack community that do output capturing rely on some "end of test" handling in testtools to dump the accumulated data. You can see this by trying a LOG.critical("hi") somewhere in the (e.g.) placement code and causing a test to fail. Dropping to a gabbi <2 makes it work again.

We're definitely not going to add testtools back in, but the test case subclass in gabbi itself may be able to handling the data gathering that's required. Some investigation required.

/cc @lbragstad for awareness