pytest: more reliable onchain tests.

We extract the tx from the logs, and then we wait until that hits
the mempool.  This is more reliable than 'sendrawtx' in the logs,
which might catch a previous sendrawtx; it's also more explicit
that we expect that tx exactly.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/utils.py

@@ -632,6 +632,20 @@ class LightningNode(object):
         if wait_for_effect:
             wait_for(lambda: self.daemon.rpcproxy.mock_counts['estimatesmartfee'] >= 3)
 
+    def wait_for_onchaind_broadcast(self, name, resolve=None):
+        """Wait for onchaind to drop tx name to resolve (if any)"""
+        if resolve:
+            r = self.daemon.wait_for_log('Broadcasting {} .* to resolve {}'
+                                         .format(name, resolve))
+        else:
+            r = self.daemon.wait_for_log('Broadcasting {} .* to resolve '
+                                         .format(name))
+
+        rawtx = re.search('.* \(([0-9a-fA-F]*)\) ', r).group(1)
+        txid = self.bitcoin.rpc.decoderawtransaction(rawtx, True)['txid']
+
+        wait_for(lambda: txid in self.bitcoin.rpc.getrawmempool())
+
 
 class NodeFactory(object):
     """A factory to setup and start `lightningd` daemons.