httpinstance: make sure NSS database is backed up
    
    The NSS database at /etc/httpd/alias is not properly initialized and backed
    up in CA-less replica promotion. This might cause the install to fail after
    previous install and uninstall.
    
    Make sure the NSS database is initialized and backed up even in CA-less
    replica promotion to fix the issue.
    
    https://pagure.io/freeipa/issue/4639
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>