gtestdbus: Properly close server connections

Otherwise g_test_dbus_down() following a g_test_dbus_stop()
will hang until it times out.

https://bugzilla.gnome.org/show_bug.cgi?id=711807
Fix desktop-app-info test

The recent change to the search scoring algorithm made
nautilus and konqueror switch places in the search results.
Update the test to reflect that.