eds: Ignore errors from unimplemented EDS methods

We can assume the methods are deliberately not implemented, so we
shouldn’t warn about them.

This complements the patch in
https://bugzilla.gnome.org/show_bug.cgi?id=731981.

https://bugzilla.gnome.org/show_bug.cgi?id=726973
eds: Bypass test failures on GTestDBus teardown

GTestDBus can sometimes fail on teardown, causing our EDS tests to
spuriously fail, and this has become a real thorn in our side. While we
wait for the proper solution to the relevant GLib bugs to be hashed out,
let’s simply exit early from the tests to ignore failures in teardown.

This will not affect (non-teardown) test failures from true positives,
as it only happens on final teardown.

https://bugzilla.gnome.org/show_bug.cgi?id=726973
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.