def cpu_usage
      result = run("cgroup", "cpuacct.usage").to_s.strip
      result.empty? ? nil : Float("%.4f" % (result.to_i / 1E9))
    end
def cpu_usage
      result = run("cgroup", "cpuacct.usage").to_s.strip
      result.empty? ? nil : Float("%.4f" % (result.to_i / 1E9))
    end
Get container cpu usage in seconds
 @return [Float]