Clean up how we signal device failure in run-webkit-tests --android.

This consolidates the logic in ChromiumAndroidDriver._abort() so
that the logging is consistent and we can track when we think the
device has failed so that we don't attempt to talk to it again.

TBR=peter@chromium.org
BUG=305040

Review URL: https://codereview.chromium.org/79453002

git-svn-id: svn://svn.chromium.org/blink/trunk@162400 bbb929c8-8fbe-4397-9dbb-9b2b20218538