cli: register event handler first, then do lookup

cli: register event handler first, then do lookup

We seem to be getting timeout for ubus wait_for calls
every now and then.

And it's not reliably reproducible.
Looking at the code the only thing that would look like
a potetntial reason, is that between the ubus_lookup() and
ubus_register_event_handler() calls, there's a very narrow
window where the event would get sent out and we would not
get it, thus having to timeout.

It doesn't look like registering the event handler first
is a big problem for the whole wait_check_object() logic.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>