The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/40e182b10320d3a8596a7a4eb87d2ec6b981bc71

commit 40e182b10320d3a8596a7a4eb87d2ec6b981bc71
Author: Shuqian Zhao <shuqianz@chromium.org>
Date: Tue Oct 11 18:55:11 2016

[autotest] Ensure one host only has one board label

Ensure one host only has one board label with it, otherwise shard-client
will crash

BUG= chromium:654100 
TEST=Test in local autotest

Change-Id: I4e9035d331d03554612ba46040d118a6807d950c
Reviewed-on: https://chromium-review.googlesource.com/396530
Commit-Ready: Shuqian Zhao <shuqianz@chromium.org>
Tested-by: Shuqian Zhao <shuqianz@chromium.org>
Reviewed-by: Dan Shi <dshi@google.com>

[modify] https://crrev.com/40e182b10320d3a8596a7a4eb87d2ec6b981bc71/frontend/afe/models.py
[modify] https://crrev.com/40e182b10320d3a8596a7a4eb87d2ec6b981bc71/frontend/afe/rpc_interface.py
[modify] https://crrev.com/40e182b10320d3a8596a7a4eb87d2ec6b981bc71/frontend/afe/models_test.py