pytest: fix flake in test_channel_lease_unilat_closes

We actually were waiting for l3 to disconnect, not l2.

But in general we should be looking for status rather than grovelling
in the logs where possible, so I changed all those.

```
2021-08-17T04:40:34.9015538Z         # l2 leases a channel from l3
2021-08-17T04:40:34.9016520Z         l2.rpc.connect(l3.info['id'], 'localhost', l3.port)
2021-08-17T04:40:34.9017570Z         rates = l2.rpc.dev_queryrates(l3.info['id'], amount, amount)
2021-08-17T04:40:34.9018724Z         l3.daemon.wait_for_log('disconnect')
2021-08-17T04:40:34.9019851Z         l2.rpc.connect(l3.info['id'], 'localhost', l3.port)
2021-08-17T04:40:34.9021467Z         l2.rpc.fundchannel(l3.info['id'], amount, request_amt=amount,
2021-08-17T04:40:34.9022865Z                            feerate='{}perkw'.format(feerate), minconf=0,
2021-08-17T04:40:34.9024000Z >                          compact_lease=rates['compact_lease'])
...
2021-08-17T04:40:34.9103422Z >           raise RpcError(method, payload, resp['error'])
2021-08-17T04:40:34.9106829Z E           pyln.client.lightning.RpcError: RPC call failed: method: fundchannel, payload: {'id': '035d2b1192dfba134e10e540875d366ebc8bc353d5aa766b80c090b39c3a5d885d', 'amount': 500000, 'feerate': '2000perkw', 'announce': True, 'minconf': 0, 'request_amt': 500000, 'compact_lease': '029a00640064000000644c4b40'}, error: {'code': 400, 'message': 'Unable to connect, no address known for peer', 'data': {'id': '035d2b1192dfba134e10e540875d366ebc8bc353d5aa766b80c090b39c3a5d885d', 'method': 'connect'}}
```

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

tests/test_closing.py

@@ -739,7 +739,7 @@ def test_channel_lease_falls_behind(node_factory, bitcoind):
 
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     rates = l1.rpc.dev_queryrates(l2.info['id'], amount, amount)
-    l1.daemon.wait_for_log('disconnect')
+    wait_for(lambda: len(l1.rpc.listpeers(l2.info['id'])['peers']) == 0)
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     # l1 leases a channel from l2
     l1.rpc.fundchannel(l2.info['id'], amount, request_amt=amount,
@@ -779,7 +779,7 @@ def test_channel_lease_post_expiry(node_factory, bitcoind):
     # l1 leases a channel from l2
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     rates = l1.rpc.dev_queryrates(l2.info['id'], amount, amount)
-    l1.daemon.wait_for_log('disconnect')
+    wait_for(lambda: len(l1.rpc.listpeers(l2.info['id'])['peers']) == 0)
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     l1.rpc.fundchannel(l2.info['id'], amount, request_amt=amount,
                        feerate='{}perkw'.format(feerate),
@@ -864,7 +864,7 @@ def test_channel_lease_unilat_closes(node_factory, bitcoind):
 
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     rates = l1.rpc.dev_queryrates(l2.info['id'], amount, amount)
-    l1.daemon.wait_for_log('disconnect')
+    wait_for(lambda: len(l1.rpc.listpeers(l2.info['id'])['peers']) == 0)
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     # l1 leases a channel from l2
     l1.rpc.fundchannel(l2.info['id'], amount, request_amt=amount,
@@ -874,7 +874,7 @@ def test_channel_lease_unilat_closes(node_factory, bitcoind):
     # l2 leases a channel from l3
     l2.rpc.connect(l3.info['id'], 'localhost', l3.port)
     rates = l2.rpc.dev_queryrates(l3.info['id'], amount, amount)
-    l3.daemon.wait_for_log('disconnect')
+    wait_for(lambda: len(l2.rpc.listpeers(l3.info['id'])['peers']) == 0)
     l2.rpc.connect(l3.info['id'], 'localhost', l3.port)
     l2.rpc.fundchannel(l3.info['id'], amount, request_amt=amount,
                        feerate='{}perkw'.format(feerate), minconf=0,
@@ -965,7 +965,7 @@ def test_channel_lease_lessor_cheat(node_factory, bitcoind, chainparams):
 
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     rates = l1.rpc.dev_queryrates(l2.info['id'], amount, amount)
-    l1.daemon.wait_for_log('disconnect')
+    wait_for(lambda: len(l1.rpc.listpeers(l2.info['id'])['peers']) == 0)
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     # l1 leases a channel from l2
     l1.rpc.fundchannel(l2.info['id'], amount, request_amt=amount,
@@ -1038,7 +1038,7 @@ def test_channel_lease_lessee_cheat(node_factory, bitcoind, chainparams):
 
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     rates = l1.rpc.dev_queryrates(l2.info['id'], amount, amount)
-    l1.daemon.wait_for_log('disconnect')
+    wait_for(lambda: len(l1.rpc.listpeers(l2.info['id'])['peers']) == 0)
     l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
     # l1 leases a channel from l2
     l1.rpc.fundchannel(l2.info['id'], amount, request_amt=amount,