Use Python 3 super(), and add self.message back to my exceptions

nilmdb/client/errors.py

@@ -9,7 +9,7 @@ class Error(Exception):
                  message = None,
                  url = None,
                  traceback = None):
-        Exception.__init__(self, status)
+        super().__init__(status)
         self.status = status     # e.g. "400 Bad Request"
         self.message = message   # textual message from the server
         self.url = url           # URL we were requesting

nilmdb/server/errors.py

@@ -3,7 +3,8 @@
 class NilmDBError(Exception):
     """Base exception for NilmDB errors"""
     def __init__(self, message = "Unspecified error"):
-        Exception.__init__(self, message)
+        super().__init__(message)
+        self.message = message
 
 class StreamError(NilmDBError):
     pass