The drone_tmp folder is deleted when there is a scheduler restart. Ideally, the content of drone_tmp/attach.xxx should be picked up by the test once the test started, so the deletion of the attach file won't cause test failure. 

In the case of server side packaging, the problem is that attache file is not copied over to container until it's setup, which takes 20-30 seconds. So there is a window that scheduler restart can fail a test using server-side packaging.

Maybe we should read the file right after the test is started.

Meanwhile, it's a race condition and shouldn't happen a lot (we only restart scheduler during push to prod). 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/38fff70fc5257cd1497455e7fbc2742a2bd47ba9

commit 38fff70fc5257cd1497455e7fbc2742a2bd47ba9
Author: Dan Shi <dshi@google.com>
Date: Mon Mar 28 20:53:18 2016

[autotest] Save control file before setting up container

This is to prevent test failure caused by missing control file.
Scheduler restart leads to all control files in drone_tmp being deleted.
Due to the long delay of setting up container when running tests with SSP,
this becomes more of an issue.

This change saves the control file to result folder before setting up
container.

BUG= chromium:598379 
TEST=local run test, unittest

Change-Id: I10a7715477ce14d3cbba5176292fc9aca19f9f2d
Reviewed-on: https://chromium-review.googlesource.com/335269
Commit-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>

[modify] https://crrev.com/38fff70fc5257cd1497455e7fbc2742a2bd47ba9/site_utils/lxc.py

Bulk verified