[autotest] Add a utility module to interact with LXC binaries.

Add a module (lxc.py) to interact with LXC binaries.

lxc_functional_test.py is a test script to test the module. It will
1. Set up base container in a tmp directory.
2. Create a test container from the base container.
3. Test site-packages and results directory can be mounted and shared between
   host and test container.
4. Run autoserv in test mode.

Also add a utility function in client/common_lib/site_utils.py to get the value
of the given argument for the function. It's used in decorator to check function
parameters.

BUG=chromium:453621
CQ-DEPEND=CL:251140

TEST=unittest,
sudo python site_utils/lxc_functional_test.py
sudo python site_utils/lxc.py -s -p /tmp/container_123
sudo python site_utils/lxc.py -s -p /tmp/container_123 -f
sudo python site_utils/lxc.py -p /tmp/container_123 -f

Change-Id: Id7b259c4bc03977974af44d6d88420b220706589
Reviewed-on: https://chromium-review.googlesource.com/247271
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
6 files changed