Add xml import back in

Erroneously removed this when adopting the introspection parser
library function.
diff --git a/rest-dbus b/rest-dbus
index ddd958b..d756dc8 100644
--- a/rest-dbus
+++ b/rest-dbus
@@ -6,6 +6,7 @@
 import json
 import os
 import sys
+from xml.etree import ElementTree
 from OpenBMCMapper import IntrospectionParser
 
 busses = {