This tidies up our testing tools a little bit. We had several
functions which through various changes ended up doing the same and
some more which did very similar stuff, so I merged them to have
things simpler. Also moved towards methods on the TestContext struct
while cleaning this up anyway, seems like this structure is going to
stay around for a bit anyway.
The intersting change is in `test_utils.rs`, everything else is just
updating callers. A few tests used example.org which I moved to
example.com to be able to re-use more configuration of the test
context.