core: include metric name in error message (#2412)

Change-Id: I8e7578fa4c5af6e8dcde04201ec7d6aa9c8f8762

Author: igorbernstein2

google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/data/v2/it/BuiltinMetricsIT.java

@@ -360,6 +360,7 @@ private ListTimeSeriesResponse verifyMetricsArePublished(
 
   private void verifyMetricsWithMetricsReader(
       ListTimeSeriesResponse response, MetricData dataFromReader) {
+
     for (TimeSeries ts : response.getTimeSeriesList()) {
       Map<String, String> attributesMap =
           ImmutableMap.<String, String>builder()
@@ -399,7 +400,8 @@ private void verifyMetricsWithMetricsReader(
       if (point.size() > 0) {
         long actualValue = (long) point.get(0).getValue().getDistributionValue().getMean();
         assertWithMessage(
-                "actual value does not match expected value, actual value "
+                ts.getMetric().getType()
+                    + " actual value does not match expected value, actual value "
                     + actualValue
                     + " expected value "
                     + expectedValue