qapi: Use OrderedDict from standard library if available

The OrderedDict class appeared in the 'collections' module
from python 2.7 onwards, so use that in preference to our
local backport if available.

Backports commit 38710a8994911d98acbe183a39ec3a53638de510 from qemu

qemu/scripts/qapi.py

@@ -18,6 +18,9 @@ import os
 import re
 import string
 import sys
+try:
+    from collections import OrderedDict
+except:
     from ordereddict import OrderedDict
 
 builtin_types = {