[Dolphin] another mode to test DP for test time saving

Set argument verify_display_switch to False to test DP without display
For this mode, once DP external display is connected, it directly
captures the image on external display (which will be default wallpaper)
and compares to golden wallpaper.

It can save test time from 28 seconds to 12 seconds.

Note: this is only valid for loopback test, not NUC test.

TEST=manual test.

Change-Id: Ib9843d648530e936439c130d54c383c51dc3297a
Reviewed-on: https://chromium-review.googlesource.com/280975
Reviewed-by: Bowgo Tsai <bowgotsai@chromium.org>
Reviewed-by: JAMES C Chen <james.c.chen@intel.com>
Tested-by: JAMES C Chen <james.c.chen@intel.com>
Commit-Queue: Pin-chih Lin <johnylin@chromium.org>
3 files changed