dev: add initial APIs to devserver to support cros auto-update.

This CL adds three APIs on devserver:
1. 'cros_au' API: to support 'start cros auto-update'.
2. 'get_au_status' API: to check the status of cros auto-update.
3. 'collect_au_log' API: to collect auto-update log from devserver.
4. 'handler_cleanup' API: delete the status file for tracking the progress of
   CrOS auto-update.
5. 'kill_au_proc' API: to kill unexpected auto-update process for DUT.

Also it updates the unittests and integration test.

The 'cros_au' API triggers a background process to support the whole
auto-update processes for a CrOS host, includes:
1. Transfer devserver/stateful update package.
2. If devserver cannot run on the host, restore the stateful partition.
3. If restore_stateful_partiton is not required, and stateful_update is
required, do stateful_update.
4. If stateful_update fails, or rootfs_update is required, do rootfs update.
5. Final check after the whole auto-update process.

TEST=Locally ran 'ds.auto_update([dut], [image_path])';
Ran 'repair' for dut from local autotest instance;
Ran unittest, devserver_integration_test.

 Changes to be committed:
	modified:   Makefile
	new file:
	new file:
	new file:
	new file:

Change-Id: I2e9c116bc1e0b07d37b540266fd252aee4fd6e84
Commit-Ready: Xixuan Wu <>
Tested-by: Xixuan Wu <>
Reviewed-by: Xixuan Wu <>
7 files changed