ipatests: tasks.py: fix ipa-epn invocation
tasks.py::ipa_epn would previously fail to invoke ipa-epn with
from_nbdays=0.
Related: https://pagure.io/freeipa/issue/8449
Signed-off-by: François Cami <fcami@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>