IPA-EPN: enhance input validation
Enhance input validation:
* make sure --from-nbdays and --to-nbdays are integer
* make sure --from-nbdays < --to-nbdays
Fixes: https://pagure.io/freeipa/issue/8444
Signed-off-by: François Cami <fcami@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>