Copy "use libcontainer" pull request
o Shamelessly copy https://github.com/jpetazzo/pipework/pull/41, and modify
  it to more simply fall-back to docker if cgroups lookup doesn't work.
o Ensure we properly test for failures when seeking data from cgroups
  or docker, to avoid silent failure due to the "set -e"
o Consolidate all indentation to use spaces instead of inconsistent tabs
Consolidagte all error, warning and debug logging, and emit to stderr