Parallel workflow execution

[AcquaDiGiorgio]

Add parallel execution at job submission by default

Tests check the following:

• If the workflow got actually executed parallely (against a sequential workflow)
• Having only a singular available core, if it acts like a sequential workflow

See #43

[aldbr]

Great! Thank you @AcquaDiGiorgio 🙂

I just have a few comments:

• We are streamlining the tests in parallel and the mandelbrot workflow will likely go away. Do you think you could get the same results using the crypto workflow? I think it contains 4 independent steps.
• Do you think we need to have a "sequential" version of the tested workflow? Naively, I think it is not necessary because it's already tested everywhere else: if dependent steps would run in parallel, other tests couldn't work.
• I think I would test the crypto workflow with taskset -c 0 and then taskset -c 0-1 for instance to demonstrate the difference in duration.

Do you have any opinion? Please let me know if you think I 'm wrong

[AcquaDiGiorgio]

Due to the nature of the crypto algortithms, it might be difficult to differentiate between a parallel and a sequential execution, in both cases they get executed extremely quick. If pi-simulate is going to stay in the future, I might be able to use it, because the size of inputs will vary the execution time.

I'm using a forced sequential workflow to be able to compare it with a parallel one that executes in one core.
If you find this test innecesary, I can completely remove it and the sequential cwl, bacause for first test, as you said, the sequential workflow can be a taskset -c 0 of the parallel one.