In editor_menu_main(), after saving a connection we wait that the
Update2() D-Bus call returns and then we copy the NMRemoteConnection
instance over to @connection.

This assumes that when Update2() returns the remote connection
instance is already updated with new settings. Indeed, on server side
the NMSettingsConnection first emits the "Updated" signal and then
returns to Update2(). However, the Updated signal doesn't include the
new setting values and so libnm has to fire an asynchronous
nmdbus_settings_connection_call_get_setting() to fetch the new
settings, which terminates after the Update2().

So, to be sure that the remote connection got updated we have also to
listen to the connection-changed signal, which is always emitted after
an update.

https://bugzilla.redhat.com/show_bug.cgi?id=1546805