Vendor libcontainer v0.0.4

Noteworthy changes:

- Add Prestart/Poststop hook support
- Fix bug finding cgroup mount directory
- Add OomScoreAdj as a container configuration option
- Ensure the cleanup jobs in the deferrer are executed on error
- Don't make modifications to /dev when it is bind mounted

Other changes in runc:

https://github.com/opencontainers/runc/compare/v0.0.3...v0.0.4

Signed-off-by: David Calavera <david.calavera@gmail.com>