pytest: be sure that we receive error on datalose failure.

It was intermittant before: I added a sleep(1) in the code before
sending the error (temporarily) to make it always triggers.

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

channeld/channeld.c

@@ -4437,6 +4437,7 @@ static void check_future_dataloss_fields(struct peer *peer,
 			take(towire_channeld_fail_fallen_behind(NULL,
 				       remote_current_per_commitment_point)));
 
+	sleep(1);
 	/* We have to send them an error to trigger dropping to chain. */
 	peer_failed_err(peer->pps, &peer->channel_id,
 			"Awaiting unilateral close");

tests/test_connection.py

@@ -3055,9 +3055,8 @@ def test_dataloss_protection(node_factory, bitcoind):
     assert not l2.daemon.is_in_log('sendrawtx exit 0',
                                    start=l2.daemon.logsearch_start)
 
-    # l1 should drop to chain, but doesn't always receive ERROR before it sends warning.
-    # We have to reconnect once
-    l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
+    # l1 should receive error and drop to chain
+    l1.daemon.wait_for_log("They sent ERROR.*Awaiting unilateral close")
     l1.wait_for_channel_onchain(l2.info['id'])
 
     closetxid = only_one(bitcoind.rpc.getrawmempool(False))