Disk space for excluded storage servers should not affect ratekeeper

If a storage server has reached 95% disk space capacity, ratekeeper will heavily throttle. However, the disk space usage for an excluded storage server will not continue to grow, being at 95% disk space capacity should not affect ratekeeper. If a single storage process reaches 95% capacity, currently we have to kill the process, but we should be able to simply exclude it to prevent ratekeeper throttling.

Start by tracing how ratekeeper uses storage-server disk capacity and how excluded storage servers are represented. Reproduce the 95% capacity scenario with an excluded server and verify that ratekeeper no longer throttles because of it, while a non-excluded server still does.

Written by the indexing model from the issue text.