pytest: fix flake in test_coin_movement_notices

We restart the nodeL if the coin_movements.py plugin hasn't processed the
notification yet, it will be incorrect:

```
>       assert account_balance(l2, chanid_1) == 100001001
E       AssertionError: assert 150_001_001msat == 100_001_001
E        +  where 150001001msat = account_balance(<fixtures.LightningNode object at 0x7f0634e1eb00>, '39ac52c818c5304cf0664940ff236c4e3f8f4ceb8993cb1491347142d61b62bc')
```

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

tests/test_plugin.py

@@ -2268,6 +2268,9 @@ def test_coin_movement_notices(node_factory, bitcoind, chainparams):
     l2.rpc.sendpay(route, payment_hash21, payment_secret=inv['payment_secret'])
     l2.rpc.waitsendpay(payment_hash21)
 
+    # Make sure coin_movements.py sees event before we restart!
+    l2.daemon.wait_for_log(f"plugin-coin_movements.py: coin movement: .*'payment_hash': '{payment_hash21}'")
+
     # restart to test index
     l2.restart()
     wait_for(lambda: all(c['state'] == 'CHANNELD_NORMAL' for c in l2.rpc.listpeerchannels()["channels"]))