[autotest] Keep platform bit for a label in shards

When we add a label to a host that is in a shard,
the platform bit of the label should be forwarded as well.

BUG=chromium:502337
TEST=puppylab. Add a platform label to a host in stumpy shard.
DEPLOY=apache

Change-Id: I12c1dfc7d9a46cda5982d687a2fd160d187582a0
Reviewed-on: https://chromium-review.googlesource.com/283943
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Mungyung Ryu <mkryu@google.com>
Tested-by: Mungyung Ryu <mkryu@google.com>
diff --git a/frontend/afe/rpc_interface.py b/frontend/afe/rpc_interface.py
index 6662d82..973bd0f 100644
--- a/frontend/afe/rpc_interface.py
+++ b/frontend/afe/rpc_interface.py
@@ -180,8 +180,9 @@
     # S2 should have the new label without any problem.
     # We ignore exception in such a case.
     rpc_utils.fanout_rpc(
-            host_objs, 'add_label', name=label.name, id=label.id,
-            include_hostnames=False, ignore_exception_if_exists=True)
+            host_objs, 'add_label', include_hostnames=False,
+            name=label.name, ignore_exception_if_exists=True,
+            id=label.id, platform=label.platform)
     rpc_utils.fanout_rpc(host_objs, 'add_label_to_hosts', id=id)
 
     add_label_to_hosts(id, hosts)