Under Postgres, this actually takes more than 2 seconds, so w2
really has timed out already:
```
time.sleep(2) # total 2
assert not w1.done()
> assert not w2.done()
E assert not True
E + where True = done()
E + where done = <Future at 0x7fe14e54fee0 state=finished raised RpcError>.done
tests/test_invoices.py:420: AssertionError
```
So space the timeouts out more, and sleep one second too short; the
.result() (which sleeps) will catch up if we were extremely slow.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
56a32c9f9b