community/py3-{celery,billiard,vine,case,amqp,pyro4,kombu,django-celery-results,flower}: move from testing

Take maintainership of:

• testing/py3-billiard
• testing/py3-vine
• testing/py3-case
• testing/py3-amqp
• testing/py3-pyro4
• testing/py3-kombu

Use gpep517 when not in use

Lint when issues occur

Move all to community