lnnode: test for failures in update channel policy

Author: pinheadmz

src/warnet/lnnode.py

@@ -90,7 +90,11 @@ def open_channel_to_tank(self, index: int, policy: str) -> str:
         raise Exception(f"Opened channel with txid {txid} not found in pending channels")
 
     def update_channel_policy(self, chan_point: str, policy: str) -> str:
-        return self.lncli(f"updatechanpolicy --chan_point={chan_point} {policy}")
+        ret = self.lncli(f"updatechanpolicy --chan_point={chan_point} {policy}")
+        if len(ret["failed_updates"]) == 0:
+            return ret
+        else:
+            raise Exception(ret)
 
     def connect_to_tank(self, index):
         tank = self.warnet.tanks[index]