Check for file permissions after the ca/cert-show is complete
    
    The commands ca-show and cert-show provide the ability to direct
    the certificate output to a file. If the requested object was
    not present then this resulted in a zero-length file.
    
    This is because the check to determine if the file was writable,
    by opening it, was done prior to the operation to retrieve
    the entry.
    
    So move the check after the data retrieval.
    
    Also convert cert-show to be more consistent with ca-show.
    
    I considered cleaning up the empty file afterward but IMHO we
    shouldn't touch the file until we're ready to write. This
    costs an API roundtrip but its a small price to pay for
    potentially protecting existing data.
    
    Fixes: https://pagure.io/freeipa/issue/9562
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>