ContainerLogger might leak FD if container launch fails.

In MesosContainerizer, if logger->prepare() succeeds but its continuation fails, the pipe fd allocated in the logger will get leaked. We cannot add a destructor in ContainerLogger::SubprocessInfo to close the fd because subprocess might close the OWNED fd.

A FD abstraction might help here. In other words, subprocess will no longer be responsible for closing external FDs, instead, the FD destructor will be doing so.