Remove docker so we can run it from within docker

[Denis Pisarev]

We can't avoid running cachepot from docker, and it uses the old docker driver that makes it impossible.

[Bernhard Schuster]

What we want here, is to be able to run integration tests from within docker ootb without extra permissions, by sidestepping it entirely. This requires refactoring the integration tests to abstract the container executor over docker, podman and no-op.