exception: Do not log PHP errors with severity DEBUG or INFO

exception: Do not log PHP errors with severity DEBUG or INFO

All PHP errors should be considered by monitoring queries
and error-rate alerts.

Levels DEBUG and INFO are for manual entries that can help in
debugging to see what path a program went down or what the
circumstances were in that code.

There is no reason to spread PHP error-types out on the full range
of PSR-3's DEBUG to ERROR spectrum. Instead, keep it within either
WARNING or ERROR, not below it.

Change-Id: I3f35a519b50aef5b93b9ab7a89a7c3e11d70681f