Make is so exceptions have some message

If you don't have a message on an exception it prints out as
nothing.  This change will default the messaqge to the class
name which should be useful.

Change-Id: Ie246b37c971e8c30752714b49aa55e69482b32e7

designateclient/exceptions.py

@@ -16,7 +16,10 @@
 
 
 class Base(Exception):
-    pass
+    def __init__(self, message=None):
+        if not message:
+            message = self.__class__.__name__
+        super(Base, self).__init__(message)
 
 
 class UnsupportedVersion(Base):