Refactor DockerWorker into ContainerWorker

Fourth part of patchset:
https://review.opendev.org/c/openstack/kolla-ansible/+/799229/


which was suggested to be split into smaller patches.

This commit refactors select methods from DockerWorker class
into ContainerWorker class. New class contains Docker independent
methods also used in Podman introduction and is inteded as a
parent class for specific worker classes.

Signed-off-by: Ivan Halomi <i.halomi@partner.samsung.com>
Co-authored-by: Martin Hiner <m.hiner@partner.samsung.com>
Change-Id: I2dd5920410dda053f2dfedc4e2666c56b1a7095a