lightningd: test that hsm_secret is as expected, at startup.

If you get the wrong hsm_secret, your node_id will change, and
peers won't know who you are, bitcoind will reject your transaction
signatures, and other madness.

Catch this as soon as it happens, by storing our node_id in the db.

Suggested-by: @cdecker, @fiatjaf
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: Config: `lightningd` will refuse to start with the wrong node_id (i.e. hsm_secret changes).

tests/test_wallet.py

@@ -1220,8 +1220,7 @@ def test_hsmtool_dump_descriptors(node_factory, bitcoind):
 
 @unittest.skipIf(VALGRIND, "It does not play well with prompt and key derivation.")
 def test_hsmtool_generatehsm(node_factory):
-    l1 = node_factory.get_node()
-    l1.stop()
+    l1 = node_factory.get_node(start=False)
     hsm_path = os.path.join(l1.daemon.lightning_dir, TEST_NETWORK,
                             "hsm_secret")
 
@@ -1248,6 +1247,7 @@ def test_hsmtool_generatehsm(node_factory):
 
     # We can start the node with this hsm_secret
     l1.start()
+    assert l1.info['id'] == '02244b73339edd004bc6dfbb953a87984c88e9e7c02ca14ef6ec593ca6be622ba7'
 
 
 # this test does a 'listtransactions' on a yet unconfirmed channel