Reduce logging level in tests

This allows tests to execute IO actions which have logging as a side
effect, without polluting the stderr too much.

A better solution would be that we have fine-grained control over
loggers, so that tests can run with their own logging, etc. etc..

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>