Fix display_HotPlugNoisy

Originally, the test generates a pulse train of width 100us. It causes interrupt
storm on squawks (with Intel i915).

Now we generate less pulses with mixed widths from 1us to ~1s. Also add a short
time sleep between sub tests to better separate them.

BUG=chromium:408376
TEST=manually run both extended and mirrored tests on squawks and peach pi and
see them passed.

Change-Id: Ic7ba3760f478f3db549c54d748774955b4960934
Reviewed-on: https://chromium-review.googlesource.com/217465
Tested-by: Hung-ying Tyan <tyanh@chromium.org>
Reviewed-by: Ting-Yuan Cheng <tingyuan@chromium.org>
Reviewed-by: Hung-ying Tyan <tyanh@chromium.org>
Commit-Queue: Hung-ying Tyan <tyanh@chromium.org>
2 files changed