Jan Tojnar authored Jul 15, 2018 and Tanu Kaskinen committed Aug 11, 2018

Previously, we used bare libdbus to detect PackageKit presence on start-up.
Since GLib contains its own independent D-Bus library and we are already
using it for invoking PackageKit, we ported the detection to GDBus too.

Because there is not any equivalent of dbus_bus_name_has_owner() in gdbus,
we replaced it with g_bus_watch_name(). As a bonus, the user interface will
be updated when PackageKit daemon starts or stops when the app is running.