Add tox infrastructure to test client wheel packages workflow:
* build client packages
* install client packages
* ipa-run-tests --ipaclient-unittests under Python 2 and 3
* pylint of client packages under Python 2 and 3
* placeholder packages work as expected
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Martin Basti <mbasti@redhat.com>
