Default generate_operator_out to py2

It doesn't work with python3 on mac!

Test: None.
Change-Id: I95147c240cc011ee9fd3eeb732f7fbe5252ec22c
diff --git a/tools/Android.bp b/tools/Android.bp
index 5093d7a..a7ed9bc 100644
--- a/tools/Android.bp
+++ b/tools/Android.bp
@@ -19,4 +19,12 @@
   srcs: [
     "generate_operator_out.py",
   ],
+  version: {
+    py2: {
+      enabled: true,
+    },
+    py3: {
+      enabled: false,
+    },
+  },
 }