initialize empty /etc/http/alias during server/replica install
    
    In order to reduce coupling between httpinstance and other service installers,
    the HTTP installer is now tasked with initialization of /etc/httpd/alias (RA
    agent database) in the beginning of server/replica installation
    
    Part of https://fedorahosted.org/freeipa/ticket/6429
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>