Change the "count_until_fail" option to gnop, know it's enables the
failing rating instead of setting them to 100%.
The original patch introduced the new flag, which sets the fail/rate to 100% after N requests.
In some cases, I don't want to have 100% of failure probabilities, I just want to start failing at some point.
For example on the early stage, I would like to allow some read/writes requests before having some requests delayed.
For example when I try to mount partition, or when I'm trying to import pool.
Other case maybe to check how scrub in ZFS will behave, on different stages.
This is allows us to cover more cases.
The previous behavior still maybe configured.