Fix certificate type error when exporting to file
Commands `ipa ca-show` and `ipa cert-show` share the same code,
this commit updates the former, closing the gap between them.
Reflecting the changes done in 5a44ca638310913ab6b0c239374f4b0ddeeedeb3.
https://pagure.io/freeipa/issue/7628
Signed-off-by: Armando Neto <abiagion@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>