Talked with developers to determine best way to verify VT2 is WAI

Summary: We can verify VT2 using keystrokes to create a file and then verify the file exists. Another way is to take screenshots, rescale, and compare which will be a less flakier version of graphics_VTSwitch.

Related bugs: crbug.com/413088

Screenshot.py is no longer in use, need to fix this before we continue with the test.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/1e7fd5f18f7e44adadb04a24735fb79ca2326af3

commit 1e7fd5f18f7e44adadb04a24735fb79ca2326af3
Author: Ruchi Jahagirdar <rjahagir@google.com>
Date: Thu Dec 01 22:21:21 2016

Modifying graphics_VTSwitch test

Now uses screenshot.py to take screenshots, no longer dependent on
gfxtest.

BUG= chromium:658882 
TEST=tested on device at desk and lab DUTs

Change-Id: I4906fbca10c3a18a482186aebadcd49a4e542d4a
Reviewed-on: https://chromium-review.googlesource.com/415610
Commit-Ready: Ruchi Jahagirdar <rjahagir@chromium.org>
Tested-by: Ruchi Jahagirdar <rjahagir@chromium.org>
Reviewed-by: Kalin Stoyanov <kalin@chromium.org>

[modify] https://crrev.com/1e7fd5f18f7e44adadb04a24735fb79ca2326af3/client/site_tests/graphics_VTSwitch/control
[add] https://crrev.com/1e7fd5f18f7e44adadb04a24735fb79ca2326af3/client/cros/input_playback/keyboard_ctrl+alt+f2
[modify] https://crrev.com/1e7fd5f18f7e44adadb04a24735fb79ca2326af3/client/site_tests/graphics_VTSwitch/graphics_VTSwitch.py
[add] https://crrev.com/1e7fd5f18f7e44adadb04a24735fb79ca2326af3/client/cros/input_playback/keyboard_ctrl+alt+f1