Catch KMSThrottlingException errors - backoff and wait in that case

We could add this error to the list of known, retryable exceptions here:

https://github.com/mapbox/kine/blob/7f505615fe3b3e9137d9188ae5bf262d4bcb7da9/lib/kcl.js#L177

They do not happen often, but when they do it's better to have the delay and retry be managed by Kine.

cc/ @mick @l-r

Start in lib/kcl.js at the linked list of known retryable exceptions and inspect how retry delays are applied. Add KMSThrottlingException to that handling, then verify that this error follows the existing delay-and-retry path.

Written by the indexing model from the issue text.