pytest: detect warnings, too.

Since we turned many errors into warnings, we want our tests to fail
when they happen unexpectedly.  We make WARNING clear in the strings
we print, too, to help out.

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

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

@@ -619,8 +619,11 @@ class PrettyPrintingLightningRpc(LightningRpc):
 
 class LightningNode(object):
     def __init__(self, node_id, lightning_dir, bitcoind, executor, valgrind, may_fail=False,
-                 may_reconnect=False, allow_broken_log=False,
-                 allow_bad_gossip=False, db=None, port=None, disconnect=None, random_hsm=None, options=None,
+                 may_reconnect=False,
+                 allow_broken_log=False,
+                 allow_warning=False,
+                 allow_bad_gossip=False,
+                 db=None, port=None, disconnect=None, random_hsm=None, options=None,
                  **kwargs):
         self.bitcoin = bitcoind
         self.executor = executor
@@ -628,6 +631,7 @@ class LightningNode(object):
         self.may_reconnect = may_reconnect
         self.allow_broken_log = allow_broken_log
         self.allow_bad_gossip = allow_bad_gossip
+        self.allow_warning = allow_warning
         self.db = db
 
         # Assume successful exit
@@ -1207,6 +1211,7 @@ class NodeFactory(object):
             'disconnect',
             'may_fail',
             'allow_broken_log',
+            'allow_warning',
             'may_reconnect',
             'random_hsm',
             'feerates',