Allow non-privileged containers to create device nodes.

Such nodes could already be created by importing a tarball to a container; now
they can be created from within the container itself.

This gives non-privileged containers the mknod kernel capability, and modifies
their cgroup settings to allow creation of *any* node, not just whitelisted
ones.  Use of such nodes is still controlled by the existing cgroup whitelist.

Docker-DCO-1.1-Signed-off-by: Kevin Wallace <kevin@pentabarf.net> (github: kevinwallace)
Add myself to AUTHORS.

Docker-DCO-1.1-Signed-off-by: Kevin Wallace <kevin@pentabarf.net> (github: kevinwallace)