pyln-testing: increase default daemon.wait() timeout.

Valgrind in CI is slow:

```
    def test_bitcoin_failure(node_factory, bitcoind):
...
        # Ignore BROKEN log message about blocksonly mode.
        l2 = node_factory.get_node(start=False, expect_fail=True,
                                   allow_broken_log=True)
        l2.daemon.start(wait_for_initialized=False)
        # Will exit with failure code.
>       assert l2.daemon.wait() == 1

tests/test_misc.py:114: 
```

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

contrib/pyln-testing/pyln/testing/utils.py

@@ -598,7 +598,7 @@ def start(self, stdin=None, wait_for_initialized=True):
             self.wait_for_log("Server started with public key")
         logging.info("LightningD started")
 
-    def wait(self, timeout=10):
+    def wait(self, timeout=TIMEOUT):
         """Wait for the daemon to stop for up to timeout seconds
 
         Returns the returncode of the process, None if the process did