Improve py2 compatibility of WMException __init__

This solves the issue 9862,
The rationale for this change is described in the
issue comments

src/python/WMCore/WMException.py

@@ -6,6 +6,8 @@
 
 """
 
+from builtins import bytes
+
 import exceptions
 import inspect
 import logging
@@ -27,7 +29,7 @@ class WMException(exceptions.Exception):
 
     def __init__(self, message, errorNo=None, **data):
         self.name = str(self.__class__.__name__)
-        if hasattr(message, "decode"):
+        if type(message) == bytes:
             # Fix for the unicode encoding issue, see #8056 and #8403
             # interprets this string using utf-8 codec and ignoring any errors
             message = message.decode('utf-8', 'ignore')
@@ -151,7 +153,7 @@ def __str__(self):
         strg += self.traceback
         strg += '\n'
         strg += WMEXCEPTION_END_STR
-        if hasattr(strg, "decode"):
+        if type(strg) == bytes:
             # Fix for the unicode encoding issue, #8043
             strg = strg.decode('utf-8', 'ignore')
         return strg