Update to libcontainer 8d1d0ba38a7348c5cfdc05aea3b

This fixes issues where the apparmor profile is not applied to processes
via docker exec.  As a side effect the parent processes were unable to
kill the additional child processes because of the profile mismatch.

Easy way to reproduce on an apparmor system:
docker run -ti debian:jessie bash
ps auxZ
- look at the labels

- in another shell
docker exec <name> sleep 1000

- go back to the first container and
ps auxZ
- make sure all processes have the correct docker-default profile

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Merge pull request #8552 from crosbymichael/update-libcontainer-oct2

Update to libcontainer 8d1d0ba38a7348c5cfdc05aea3b