This means running 3 bitcoinds, which is slow enough to start on my laptop
that I need to increase the startup wait for 30 to 60 seconds, and similarly
the test.sh check loop.
Before: real 13m42.868s
After: real 8m19.563s (make -j3)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>