This patch adds SELinux labeling support.

The basic idea is to run the process with an SELinux label and to label all the content with
a mount label.  Any temporary file systems created need to be mounted with the mount label.

For now the user can override the process label by specifying

-Z With a string of space separated options.

-Z "user=unconfined_u role=unconfined_r type=unconfined_t level=s0"

Would cause the process label to run with unconfined_u:unconfined_r:unconfined_t:s0"

By default the processes will run execute within the container as svirt_lxc_net_t.
All of the content in the container as svirt_sandbox_file_t.

The process mcs level is based of the PID of the docker process that is creating the container.