Setup standard /dev symlinks

After copying allowed device nodes, set up "/dev/fd", "/dev/stdin",
"/dev/stdout", and "/dev/stderr" symlinks.

Docker-DCO-1.1-Signed-off-by: Bernerd Schaefer <bj.schaefer@gmail.com> (github: bernerdschaefer)
[rebased by @crosbymichael]
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #5807 from crosbymichael/dev-symlinks

Setup standard /dev symlinks