We assume that because we've told l3 to shut down, l2 already sees it
as disconnected. But CI is ...slow... today!
```
# `l3` is disconnected and we can't send messages to it
> assert(not l2.rpc.listpeers(l3.info['id'])['peers'][0]['connected'])
E assert not True
tests/test_misc.py:2218: AssertionError
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>