[autotest] audio_AudioBasicHDMI: do extra plug/unplug to detect HDMI

For boards using exynos HDMI driver, it has problem detecing HDMI audio.
The workaround is to plug/unplug several times.

BUG=chromium:450101
TEST=run audio_AudioBasicHDMI test on peach_pit

Change-Id: I4c1d9c97be565cbd409dd97a3a3dce3cb8056814
Reviewed-on: https://chromium-review.googlesource.com/324678
Commit-Ready: Cheng-Yi Chiang <[email protected]>
Tested-by: Cheng-Yi Chiang <[email protected]>
Reviewed-by: Cheng-Yi Chiang <[email protected]>
2 files changed