use AddError everywhere (#2372)

plugins/inputs/sqlserver/sqlserver.go

@@ -79,20 +79,19 @@ func (s *SQLServer) Gather(acc telegraf.Accumulator) error {
 	}
 
 	var wg sync.WaitGroup
-	var outerr error
 
 	for _, serv := range s.Servers {
 		for _, query := range queries {
 			wg.Add(1)
 			go func(serv string, query Query) {
 				defer wg.Done()
-				outerr = s.gatherServer(serv, query, acc)
+				acc.AddError(s.gatherServer(serv, query, acc))
 			}(serv, query)
 		}
 	}
 
 	wg.Wait()
-	return outerr
+	return nil
 }
 
 func (s *SQLServer) gatherServer(server string, query Query, acc telegraf.Accumulator) error {