Change log level of several logging events

These logging events are recurring. As a result logging at INFO level
spams the user of the metrics library with periodic logs. Changing them
to FINE level so that the user can eaisily filter these logs out.

Author: jianglai

metrics/src/main/java/com/google/monitoring/metrics/MetricExporter.java

@@ -54,9 +54,9 @@ protected void run() throws Exception {
     logger.info("Started up MetricExporter");
     while (isRunning()) {
       Optional<ImmutableList<MetricPoint<?>>> batch = writeQueue.take();
-      logger.info("Got a batch of points from the writeQueue");
+      logger.fine("Got a batch of points from the writeQueue");
       if (batch.isPresent()) {
-        logger.info("Batch contains data, writing to MetricWriter");
+        logger.fine("Batch contains data, writing to MetricWriter");
         try {
           for (MetricPoint<?> point : batch.get()) {
             writer.write(point);

metrics/src/main/java/com/google/monitoring/metrics/MetricReporter.java

@@ -84,7 +84,7 @@ public MetricReporter(
 
   @Override
   protected void runOneIteration() {
-    logger.info("Running background metric push");
+    logger.fine("Running background metric push");
 
     if (metricExporter.state() == State.FAILED) {
       startMetricExporter();

stackdriver/src/main/java/com/google/monitoring/metrics/stackdriver/StackdriverWriter.java

@@ -214,7 +214,7 @@ public void flush() throws IOException {
     for (TimeSeries timeSeries : timeSeriesList) {
       pushedPoints.increment(timeSeries.getMetricKind(), timeSeries.getValueType());
     }
-    logger.info(String.format("Flushed %d metrics to Stackdriver", timeSeriesList.size()));
+    logger.fine(String.format("Flushed %d metrics to Stackdriver", timeSeriesList.size()));
   }
 
   /**