provide an example SELinux policy for older releases

provide an example SELinux policy for older releases

The virtd_lxc_t type provided by the default RHEL/CentOS/Oracle 6.5
policy is an unconfined_domain(), so it doesn't really enforce anything.
This change will provide a link in the documentation to an example
policy that does confine containers.

On more recent distributions with new enough policy, it is recommended
not to use this sample policy, but to use the types already available
on the system from /etc/selinux/targeted/contexts/lxc_contexts, ie:

process = "system_u:system_r:svirt_lxc_net_t:s0"
file = "system_u:object_r:svirt_sandbox_file_t:s0"

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>