Fixed parameter used for format string in CIM exception raised in moc…

…k support.

A CIMError exception raised in the mocked ModifyInstance operation specified
`p.name` when `p` was actually already a string with the property name.

Signed-off-by: Andreas Maier <andreas.r.maier@gmx.de>

pywbem_mock/_wbemconnection_mock.py

@@ -2050,7 +2050,7 @@ def _fake_modifyinstance(self, namespace, **params):
             if p in modified_instance:
                 raise CIMError(CIM_ERR_INVALID_PARAMETER,
                                'ModifyInstance cannot modify key property %s' %
-                               (p.name))
+                               p)
 
         # remove any properties from modified instance not in the property_list
         if property_list: