This pull request fixes two issues in `RateLimiter` that caused
excessive rate-limiting to take place:

- c19083a35c89a22395595f8934c117a14943ed24 fixes a mistake that caused
us to load buckets from the database incorrectly and set the
`refill_time_per_token` to equal the `refill_duration`. This was the
primary reason why rate limiting was acting oddly.
- 34b88d14f6d9fde4d967554fc2e81498c1be3e26 fixes another slight logic
error that caused tokens to be underprovisioned. This was minor compared
to the bug above.

Release Notes:

- N/A