Don't consider devices with their screens off for running layout tests.

Running layout tests with the device's screen off will result in a hard
to understand NPE in the Android framework itself. Avoid this by
not considering devices with their screen off in the first place.

This patch makes the layout test runner more verbose about devices which
aren't being included in running tests by outputting each skipped device
together with the reason.

BUG=232044

Review URL: https://chromiumcodereview.appspot.com/23125016

git-svn-id: svn://svn.chromium.org/blink/trunk@156627 bbb929c8-8fbe-4397-9dbb-9b2b20218538