[phone screen] Turn phone screen on for instrumentation tests

[screen] Turn phone screen on for instrumentation tests

This CL works with provision_devices, which set devices disable the lock
screen. This ensures the provision devices phone screen on for each instrumentation test.

BUG=715583

[shenghuazhang, 2017-05-17 01:59:51]

shenghuazhang@chromium.org changed reviewers:
+ jbudorick@chromium.org

[jbudorick, 2017-05-17 03:15:50]

Per discussion on the bug: this is a good start, but we should also ensure this
behaves well in the non-provision (i.e. lock screen enabled) case by raising a
clear error if we can't turn the screen on.