Performance improvement using in-operator for hash lookups

Just a small cleanup for the existing occurrences.

Using the in-operator for hash lookups is faster than using .has_key()
http://stackoverflow.com/questions/1323410/has-key-or-in

lib/ansible/modules/packaging/os/rhn_register.py

@@ -163,7 +163,7 @@ class Rhn(RegistrationBase):
         def get_option_default(self, key, default=''):
             # ignore pep8 W601 errors for this line
             # setting this to use 'in' does not work in the rhn library
-            if self.has_key(key):
+            if key in self:
                 return self[key]
             else:
                 return default