util/log: silence logging tests when they succeed
util/log: silence logging tests when they succeed

Minor refactor while I'm here.

paperstreet/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,maxlang/cockroach,petermattis/cockroach,glycerine/cockroach,glycerine/cockroach,maxlang/cockroach,veteranlu/cockroach,petermattis/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,petermattis/cockroach,maxlang/cockroach,veteranlu/cockroach,petermattis/cockroach,petermattis/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,cockroachdb/cockroach,veteranlu/cockroach,paperstreet/cockroach,maxlang/cockroach,paperstreet/cockroach,maxlang/cockroach,cockroachdb/cockroach,glycerine/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,paperstreet/cockroach,paperstreet/cockroach,cockroachdb/cockroach,veteranlu/cockroach,petermattis/cockroach,cockroachdb/cockroach,petermattis/cockroach,glycerine/cockroach,glycerine/cockroach,glycerine/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,maxlang/cockroach,petermattis/cockroach,glycerine/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,maxlang/cockroach,glycerine/cockroach,veteranlu/cockroach,paperstreet/cockroach,maxlang/cockroach