python: Ensure screen on during test

When doing instrumentation test, it will run shell stop and start after
installing packages. If the screen unlock method is not none, the screen
will be in lock state, and test would fail for some cases.
This CL would set screen unlock method to none right after flashing
image to fix this.

Some other fixes:
1. Add an option to designate device when installing apk.
2. Fix bug when feeding --devices
aosp-stable: Correct the way to set screen lock to none
uitl.py: Add function to check screen