Treat ErrorBusy in SQLite differently

[pkravchuk]

Right now all SQLError are treated the same way and we retry a configured number of times. Maybe it makes sense to inspect SQLError and on sqlError = ErrorBusy just retry indefinitely (or use timeout) and maybe more often without writing warnings to the log?

I guess I have no idea how often this error arises but given that dbRetries is configurable, it seems that it is often enough, and sometimes a lot of retries is required.