Generate SSL keys on service start
    
    This defers the creation of self-signed SSL certificates to the
    first time that httpd starts up. This has several advantages:
    
    * Waiting until the first boot will help avoid some issues with
      limited entropy in the install process.
    * The certificates can be regenerated automatically whenever they
      are removed, which helps with tools such as virt-sysprep
    * The certificates are now generated by SSCG, which produces a
      limited-trust CA alongside it that can be safely imported by a
      client.
    
    For more information on SSCG, see:
    https://sgallagh.wordpress.com/2016/05/02/self-signed-ssltls-certificates-why-they-are-terrible-and-a-better-alternative/
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>