Timeout for long running Step Intialization

[kcmannem]

With the addition of contexts to the garden/baggageclaim clients. We're now able to clean up more reliably or remotely cancel a fork of the code when needed.

We have also introduced speed improvements to streaming; to the point where strabo takes around 2.5 mins to initialize. This is the worst case scenario of how long a task may take to initialize. This gives us the tolerance to add a timeout (~30 mins is generous first guess) for the whole initialization portion of step execution.

We currently place context.Todo() in the places we'd have to add this timeout in our add_context pr.

[ddadlani]

Keep in mind that some Concourse instances are run in environments with high network latency. It may be too much to shorten the timeout so aggressively. We can definitely thread aborting and idle timeouts all the way down to Baggageclaim/Garden.

[ddadlani]

It would be nice if we can retry the step on another worker if the initialization times out, but that might be another piece of work entirely.