Instead of manually running and managing Tracker daemon processes
manually in the test, we now rely on our private D-Bus daemon to
do so.

This makes the test environment more like a real Tracker deployment.

Log output from the D-Bus daemon is now captured and output through
the Python logging system. This allows for finer-grained filtering
of output from the tests themselves and from the Tracker daemons.

Some test code is changed to support the new model.