templates: CentOS fixes

templates: CentOS fixes

Issues fixed:
- lxc-centos died about a missing /run directory
- lxc-centos complained about some config files it couldn't modify
- the new container got stuck at startup time for a minute
  (literally), waiting for systemd-remount-fs startup script

Of course it still works for RHEL 6, CentOS 6 and 7 as well. I did not
verify earlier CentOS or RHEL releases.

Signed-off-by: Harald Dunkel <harald.dunkel@aixigo.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>