Add device reboot and state management support.

DeviceManager is now responsible for device state tracking and operations that
can disrupt a device's state including reboots.

Also add:
 - method for fastboot commands
 - kill logcat thread when cancelled
 - adjust logcat logs to limit spam
 - fix test timeout handling - broke this in previous commit
 - change RunUtil run os command to return stdout output
 - misc test log cleanup
 - change host tests to use xml results, and give default output dir

Change-Id: I199d02c34cff8e4107626dab017fad335d464042
16 files changed