[PROVISIONING] prepare main to enable extending dbus api outside of main.c

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[PROVISIONING] enable extending dbus api outside of main.c

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>
[PROVISIONING] implement org.freedesktop.DBus.Introspectable.Introspect

Signed-off-by: Jarko Poutiainen <Jarko.Poutiainen@oss.tieto.com>