By policy, our stub hsmd accepts everything: openingd is supposed to
sort this out (or use VLS for a real HSM implementation!).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: Config: the node no longer crashes if you set `watchtime-blocks` to 0 (which is fine for testing: don't do this on mainnet!).