spec: have the scripts depend on py3 packages
When building for Fedora, we have with_python3 set to 1 by
default. Therefore, when such build is performed, have the
scripts depend on python3 packages instead of python2 (the
previous state was the scripts depended on both Python versions).
https://pagure.io/freeipa/issue/4985
Reviewed-By: Tomas Krizek <tkrizek@redhat.com>