Task setup scripts should run with a timeout

[ranweiler]

If a task has a setup script and it hangs, we don't time out until NODE_EXPIRATION_TIME of 1 hour expires, and the node gets reimaged. The error messages around this can be confusing

Instead, have a setup script-specific timeout that defaults to something reasonable. Ideally this would be set per-colocated task set. However, for now, it must never exceed NODE_EXPIRATION_TIME.