Fix logging calls

Author: alexander-yevsyukov

datastore/src/test/java/io/spine/server/storage/datastore/BigDataTester.java

@@ -109,7 +109,7 @@ public void testBigDataOperations(RecordStorage<I> storage) {
                         writeTime));
         }
 
-        log().debug("Writing took {} millis.", writeTime);
+        _debug().log("Writing took %d millis.", writeTime);
 
         try {
             Thread.sleep(1000);

stackdriver-trace/src/main/java/io/spine/server/trace/stackdriver/AsyncTraceService.java

@@ -44,7 +44,7 @@ final class AsyncTraceService implements TraceService, Logging {
     public void writeSpans(BatchWriteSpansRequest request) {
         client.batchWriteSpansCallable()
               .futureCall(request)
-              .addListener(() -> log().debug("Submitted {} spans", request.getSpansCount()),
+              .addListener(() -> _debug().log("Submitted %d spans.", request.getSpansCount()),
                            directExecutor());
     }