httpd config: include ServerName directive
    
    This adds a ServerName line to the httpd config generated by
    ipsilon-server-install. As documented by Apache, not including
    this causes Apache to auto-detect it, and it will often get it
    wrong.
    
    Doing this is a bit "aggressive" because it's a directive that
    can only be specified once and the last specification of it wins,
    so this could theoretically surprise an admin. In practice I
    don't really think it's a problem, though, I don't really think
    people are in the habit of deploying authentication services on
    shared hosts or anything like that. It probably doesn't do a
    whole lot on an Ipsilon server anyhow, but it *is* used in the
    SSL redirect block we write into the file, so if it's not set
    correctly, that redirect block won't work right.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>