Add new interfaces for label/selinux

We need the ability when using --ipc container:ID to match the SELinux label of the
container that the new container is sharing a label with.

Also add the ability to get the option to disable SELinux labeling for a container.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Merge pull request #247 from rhatdan/selinux

Add new interfaces for label/selinux