Allow each instance to support a zone list instead of a single zone.
Each slave is set for only one defined zone.

Tests added:
- connexion parameters
- monitor url
- slaves instanciation

Adds connexion parameters:
- ipv6
- port
- ipv4

Upgrade dnspython from 1.15.0 to 1.16.0

Removes unused parameters in instance-powerdns-replicate.cfg.jinja:
- private-ipv4
- public-ipv4
- domain

Remove method `generateHashFromFiles` in all file `test.py`, import it from `slapos.recipe.librecipe`.

/reviewed-on nexedi/slapos!617

Improved supervisord management is critical for maintenance of instances
between tests.