Pipelines with Cycles: e2e testing, and pipeline validation

[juliev0]

Fixes: #934

We will allow Cycles in Pipelines as long as there's no Reduce Vertex at the point of the Cycle or to the right of it (to avoid issues of late data after close-of-book).

This PR includes:

• e2e tests of valid Cycles
• Validation to prevent invalid Cycles

As a side note, I have observed how the cycle looks in the UI, and I believe this does need modification (i.e. if Vertex A sends to Vertex B, but Vertex B cycles back to A, there should probably be a second line (edge); and if Vertex B cycles to itself, that probably needs a line (edge))

[juliev0]

I think this is failing because maybe the image for this hasn't been published to quay.io?

[vigith]

Can you add one spec to examples/ folder which will include both cycle-to-self and cycle-to-prev ?

[juliev0]

Can you add one spec to examples/ folder which will include both cycle-to-self and cycle-to-prev ?

I added one for each - is that okay?

[vigith]

NIT: what will be the error for this func? is it only "no vertex found", isn't it already covered in 320?

[juliev0]

Yes. Well, I suppose there's nothing to prevent getCycles() from being called from somewhere else, so for completeness I think I'll leave it in.