Allow configuration of errors that shouldn't be replayed

### WHAT

Small PR. Some errors that happen on a slave, we don't want to replay on master. Right now we have one such error hardcoded to not replay (a Mysql2 Timeout Error), but we need to add another. This PR makes that list of errors & messages configurable, with a default to the current Mysql2 Timeout Error.

### HOW

Set SlavePools.config.no_replay_on_master = {ErrorClass => ['message regex']}