pytest: make test_gossip_no_empty_announcements robust when update delayed.

In this test we tell l3 to disconnect on sending WIRE_CHANNEL_ANNOUNCEMENT.
This is hit by gossipd (to disconnect from l2) but *also* channeld to
disconnect from l4.  That's OK, because normally by this point l4 has
sent its real channel_update.

However, the next patch introduces a delay in sending channel_updates,
meaning l4 hasn't sent it yet.  If l3 doesn't reconnect to l4, we
never get the channel_update and the test which expects l1 to eventually
see both sides of the channel fails.

So we manually reconnect then.  Note that we remove the redundant
'dev-no-reconnect' option from l2: it's added automatically as it
doesn't set 'may_reconnect'.

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

tests/test_lightningd.py

@@ -2935,11 +2935,12 @@ class LightningDTests(BaseLightningDTests):
     def test_gossip_no_empty_announcements(self):
         # Need full IO logging so we can see gossip
         l1 = self.node_factory.get_node(options={'log-level': 'io'})
-        l2 = self.node_factory.get_node(options={'log-level': 'io',
-                                                 'dev-no-reconnect': None})
+        l2 = self.node_factory.get_node(options={'log-level': 'io'})
         # l3 sends CHANNEL_ANNOUNCEMENT to l2, but not CHANNEL_UDPATE.
-        l3 = self.node_factory.get_node(disconnect=['+WIRE_CHANNEL_ANNOUNCEMENT'])
-        l4 = self.node_factory.get_node()
+        l3 = self.node_factory.get_node(disconnect=['+WIRE_CHANNEL_ANNOUNCEMENT'],
+                                        options={'dev-no-reconnect': None},
+                                        may_reconnect=True)
+        l4 = self.node_factory.get_node(may_reconnect=True)
 
         # Turn on IO logging for gossipds
         subprocess.run(['kill', '-USR1', l1.subd_pid('gossipd')])
@@ -2956,6 +2957,11 @@ class LightningDTests(BaseLightningDTests):
         # 0x0100 = channel_announcement, which goes to l2 before l3 dies.
         l2.daemon.wait_for_log('\[IN\] 0100')
 
+        # l3 actually disconnects from l4 *and* l2!  That means we never see
+        # the (delayed) channel_update from l4.
+        wait_for(lambda: not l3.rpc.listpeers(l4.info['id'])['peers'][0]['connected'])
+        l3.rpc.connect(l4.info['id'], 'localhost', l4.port)
+
         # But it never goes to l1, as there's no channel_update.
         time.sleep(2)
         assert not l1.daemon.is_in_log('\[IN\] 0100')