Only log an informational message when a set read-timestamp is older than the oldest timestamp.

In this example, an error message is being logged when the read timestamp is behind the oldest timestamp, which ends up going through the WT error handler.

This affects MongoDB because we log that at the highest level, "E", and is reported as a fatal error even though it is a routinely handled error.

One suggestion would be to have these errors logged as messages instead of errors. They are helpful for debugging purposes, but do not need to be reported as errors.