tracker: Ensure the Tracker connection is disposed in test teardown

This was causing the Tracker tests to fail.
tracker: Ensure all properties of Trf.Persona are initialised

The nickname and is-favourite properties were not being initialised on
construction, so if Trf.Persona.nickname was accessed before being set,
it would return null, which is invalid.
tracker: Standardise the TestCase set up procedure

Make it match the EDS one so we’re not doing heavyweight IPC in the
constructor.