Investigate reducing the amount of error level log statements.

[jstenback]

wpt.fyi tends to write a fair bit of unnecessary error level log entries, for things that one can argue are errors at higher levels of the app, but not necessarily at lower levels of the app. For instance, certain queries return no results, and that triggers errors in the services logs. And some levels of caching refuse to cache empty results, and that triggered errors as well (some of that was recently fixed). Similarly we throw HTTP error codes in cases where it may be better to simply return empty results with a success code to the caller to avoid more unnecessary noise in our logs. These errors don't necessarily hurt anything, but they trigger alerts and interrupt those who keep the site running. Sometimes those alerts are valid and do require attention, but often the alerts need no action, yet figuring that out takes time, sometimes quite a bit of time. We should investigate the source of the logged errors that really are not errors and need no action, and reduce their severity to warnings etc. Some of this may affect how the front end app behaves, i.e. if we change HTTP status codes etc, and if so, we should evaluate best paths forward in those cases.