standardize chown operations to either extend_start or config.json

This review raised an important question:
https://review.openstack.org/#/c/429358/

Should we deprecate chown in extend_start or deprecate chown in config.json. Since there is a deprecation policy, we need to first contact the operators list and see if the deprecation would cause any hassle for operators. If operators end up wanting both models, we should standardize in the kolla-code base atleast.