reduce vnode_management_timer to speed up handoff

The test often takes four minutes to run successfully with defaults.
Reducing the management timer brings the happy case down to a minute.

In fact, the time from the moment the request version is confirmed as renegotiated to the time that handoff completes is now about 25 seconds.

The failure path is still ~5 minutes, but if we know that the happy path should succeed *much* faster, maybe we can heuristically improve that.