Add --cn option to cert-status
    
    Add the 'cacn' option to the cert-status command.  Right now there
    is nothing we need to (or can) do with it, but we add it anyway for
    future use.
    
    Fixes: https://fedorahosted.org/freeipa/ticket/5999
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>