Right now, we're violating the Liskov substitution principle by deriving from `Orchestrator` but `process` takes a sub class of `Completion`:
See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
The idea is to make Orchestrator a type constructor with `CompletionT` as argument, but this is not supported by mypy: https://github.com/python/typing/issues/548
Signed-off-by: Sebastian Wagner <sebastian.wagner@suse.com>