A huge number of goroutines would build up from various monitors
When creating test filesystems provide a context so they can shut down when no longer needed.
* Fix cases where minimum timeout > default timeout.
* Add defensive code for too small/negative timeouts.
* Never set timeout below the maximum value of a request.
* Protect against (unlikely) int64 wraps.
* Decrease timeout slower.
* Don't re-lock before copying.
