gather info on jump-to-80% issues

This ticket is now for gathering additional info and feedback about the category of jump-to-80% bootstrap reporting problems.

background:

If enough existing directory information is available, the bootstrap progress as reported to the logs and the control connection jumps from 0% to 80% almost immediately. This is misleading and causes user frustration, as reported by Linda's study.

When bootstrapping with existing directory information, we should rescale the progress numbers so they advance on something resembling a linear time scale, which is probably closer to what users expect to see.