ACCUMULO-3321 Logging ThriftScanner exceptions at WARN instead of debug

This is tricky. In the case that a tserver fails, this would cause logging on the client. Ideally, the system will recover from a tserver failure and the client wouldn't even have to know that a failure happened. Might it make more sense to leave this at debug for the first N occurrences for a server and then elevate it to warn at the N+1th time?