Don't run kra.configure_instance if not necessary
    
    If kra should not be set up, don't run the code as it would only
    prolong the installations.
    
    Previously, krainstance configuration would be performed just to
    export the client certificate and private key to authenticate to
    certificate server. This is now performed somewhere else therefore
    there's no need to run KRAInstance.configure_instance.
    
    The kra.install() method still performs actions on replicas and
    we're keeping it in server installer to conform to the installers
    design.
    
    https://fedorahosted.org/freeipa/ticket/5695
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>