Fix the order in which <identity/> and <feature/> tags are sent on disco#info

The identities should all be at the start, and features at the end, so we
just prepend the identity on add_identity, and append features on
add_feature

slixmpp/plugins/xep_0030/stanza/info.py

@@ -120,7 +120,7 @@ class DiscoInfo(ElementBase):
                 id_xml.attrib['{%s}lang' % self.xml_ns] = lang
             if name:
                 id_xml.attrib['name'] = name
-            self.xml.append(id_xml)
+            self.xml.insert(0, id_xml)
             return True
         return False