Specify error produces by invocation when awaited task fails

[Gozala]

We have been implementing some promise pipeline logic and realized that it would be a good idea for invocation spec to define what happens when awaited task fails.

I think general assumption is that errors should propagate to tasks that depend on them, however I wold expect that awaiting task would get it's own receipt. I think it would be good idea to also cover in spec what the error looks like when awaited task fails.