Update libcontainer to 68ea1234a0b046803aacb2562df

Signed-off-by: Michael Crosby <michael@docker.com>
Ensure thread is locked in sysinit for docker

Signed-off-by: Michael Crosby <michael@docker.com>
Merge pull request #7407 from crosbymichael/update-libcontainer-aug1

Update libcontainer to version 68ea1234a0b046803aacb2562df0da1