## Problem
Ahead of enabling eviction in the field, where it will become the
normal/default mode, let's enable it by default throughout our tests in
case any issues become visible there.
## Summary of changes
- Make default `extra_opts` for safekeepers enable offload & deletion
- Set low timeouts in `extra_opts` so that tests running for tens of
seconds have a chance to hit some of these background operations.
John Spray
b461755326