qapi: ensure stable sort ordering when checking QAPI entities

Some early python 3.x versions will have different default
ordering when calling the 'values()' method on a dict, compared
to python 2.x and later 3.x versions. Explicitly sort the items
to get a stable ordering.

Backports commit f7a5376d4b667cf6c83c1d640e32d22456d7b5ee from qemu

qemu/scripts/qapi.py

@@ -1684,7 +1684,7 @@ class QAPISchema(object):
                 assert False
 
     def check(self):
-        for ent in self._entity_dict.values():
+        for (name, ent) in sorted(self._entity_dict.items()):
             ent.check(self)
 
     def visit(self, visitor):