Currently if you turn on --net=host on a rootless container
and have selinux-policy installed in the image, tools running with
SELinux will see that the system is SELinux enabled in rootless mode.
This patch mounts a tmpfs over /sys/fs/selinux blocking this behaviour.
This patch also fixes the fact that if you shared --pid=host we were not
masking over certin /proc paths.
Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>