Chameleon: Implement display_HotPlugAtSuspend test

This change implements the display_HotPlugAtSuspend test which remotely
emulates external display hot-plug during suspend using Chameleon board.

The configs it tests are:
  (plugged_before_suspend, plugged_after_suspend, plugged_before_resume):
    (True, True, True)
    (True, False, False)
    (True, False, True)
    (False, True, True)
    (False, True, False)

It verifies DUT behavior response to these configs.

BUG=chromium:343790
TEST=manaul
$ test_that --fast --args "chameleon_host=$CHAMELEON_IP" $DUT_IP \
      e:display_HotPlugAtSuspend.*

Change-Id: I1b8515c7cebbb56e8a2290d6014947aabc046794
Reviewed-on: https://chromium-review.googlesource.com/186347
Reviewed-by: Wai-Hong Tam <waihong@chromium.org>
Commit-Queue: Wai-Hong Tam <waihong@chromium.org>
Tested-by: Wai-Hong Tam <waihong@chromium.org>
5 files changed