jsonclient backoff is never reset

There are no calls to `jsonclient.(*backoff).decreaseMultiplier()` anywhere but in tests, so after a few `set` invocations, `multiplier` reaches 8 (`maxMultiplier`) and then always returns 128s. This means that after a bit in production, JSONClient will wait 128s upon every network error.

Search the Go code for `jsonclient.(*backoff)`, `set`, and `decreaseMultiplier`, then read the existing backoff tests first. Determine where the multiplier should be reduced or reset in production and add regression coverage showing it does not remain at `maxMultiplier` after repeated operations.

Written by the indexing model from the issue text.