Make it possible to run logical identical luigi tasks multiple times in the same python interpreter

[tkilias]

Background:

• sometimes we want to execute logical identical tasks (this means the values of all significant parameters are equal) multiple times in the same python interpreter, for example for tests or in case the result is not deterministic, ...
• However, luigi is original a workflow management system doesn't want to rerun tasks if their input parameters have the same values
• Usually, we don't need the reruns in the same invocation

Possible solution

• Because we only need the reruns between different invocations of luigi, we could introduce a new significant parameter job_id which is usually inherited from the calling tasks or given by the creator of the root task
• The inheritance from the calling tasks allows an easy pass-through of the job_id through the task hierarchy
• Letting the creator give the root task the job_id, lets the creator decide which behavior he needs.
• An example for this can be found in https://github.com/exasol/integration-test-docker-environment/pull/77/files#diff-d42a1e87a1734995ecb539bd44cc24dc5c44338255d6ef596796502c8ca6fe31
• Alternatives are described here: https://stackoverflow.com/questions/34613296/how-to-reset-luigi-task-status
• However, using explicit job_ids has the advantage that your logs and outputs for the old run still exist after a rerun
• Also, this could replace in many case the job_id_config which is a global variable with many drawbacks.

[tomuben]

Fixed with #122