Enable selinux in containers

Enable selinux in containers

We cannot use the --selinux-enabled docker daemon option on CentOS/RHEL 7.3.
It will fail if security_inode_copy_up is not found in the kernel symbols:
https://github.com/projectatomic/docker/blob/docker-1.12.6/daemon/daemon_unix.go#L661
NB this has been reduced to a warning upstream:
https://github.com/moby/moby/commit/885b29df096db1d6746ece4b3a298a1ffe85716d

Instead this just bind mounts /sys/fs/selinux in containers-common.yaml.

Everything appears to work at initial glance. Pingtest succeeds, and
live-migration between baremetal and containerized computes works.

Change-Id: I018221bf7ae9ab9ece193b55f1ce31eb1591046c
Closes-bug: #1715171
(cherry picked from commit 520f889a31f1ea6ee2bad86d1dbb3c0435604d10)