These exception are now used
- `CertAPISystemError` should be used for sentinel-internal errors
  - its child `InvalidRedisDataError` is risen when validation of data
    saved in Redis failes
- `RequestConsistencyError` should be used for client request that cant be
   processed
- `RequestProcessError` should be used for client request that can be processed,
   but the provided data is invalid, including checker/CA authentication
   failure

Among these exception the logging should be done this way:
- `RequestConsistencyError` and `RequestProcessError` should be logged on it's
  first occurence with levels `debug`, `info` and `warning` for most severe
  cases
- `CertAPISystemError` should be logged centrally in one place with levels
  `error` for most cases and `critical` when the application needs to stop
- `InvalidRedisDataError` is never logged