make httpbin bind on both ipv4 and ipv6 (istio#52346)

Author: leosarra

samples/httpbin/httpbin.yaml

@@ -60,7 +60,7 @@ spec:
         command:
         - gunicorn
         - -b
-        - 0.0.0.0:8080
+        - "[::]:8080"
         - httpbin:app
         - -k
         - gevent