Unref async results after calling g_simple_async_result_complete_in_idle()

All async results were leaked, since g_simple_async_result_complete_in_idle()
takes a new reference rather than assuming the ref passed in.

https://bugzilla.gnome.org/show_bug.cgi?id=738246
Unref result of g_async_result_get_source_object()

g_async_result_get_source_object() returns a reference that must be
unreferenced.

https://bugzilla.gnome.org/show_bug.cgi?id=738246
Don't leak result of g_dbus_connection_new_for_address_finish()

g_dbus_connection_new_for_address_finish() returns a new reference;
we can't simply ignore the returned connection, even though it is also
passed in as the source object of the GAsyncReadyCallback.

https://bugzilla.gnome.org/show_bug.cgi?id=738246