It seems to reliably be getting a SIGTERM after 17-18 minutes:
```
[gw1] [ 91%] PASSED tests/test_plugin.py::test_forward_event_notification
Error: Process completed with exit code 143.
```
Perhaps this is out of mem? So, try -n2. We also make the configure
line explicit, rather than relying on environment vars (we should probably
do this for the other cases, too)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
55d6eb6762