Add back subprocess42.call_with_timeout().
Add back subprocess42.call_with_timeout().

It happens call_with_timeout() is still used. Rewrite it using the new
communicate() timeout functionality.

R=vadimsh@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1408743002

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py