DropWizardMetricMaker: Improve error message when metric name is invalid

In case the metric name is invalid, the stack trace only contains the
required pattern but not the name itself.

Add the metric name to the message so that the stack trace is more
informative.

Change-Id: If1750a46e7d1e513d3d372212b8a95c89f682da0
Signed-off-by: Eryk Szymanski <eryksz@gmail.com>

gerrit-server/src/main/java/com/google/gerrit/metrics/dropwizard/DropWizardMetricMaker.java

@@ -339,7 +339,8 @@ public class DropWizardMetricMaker extends MetricMaker {
   private static void checkMetricName(String name) {
     checkArgument(
         METRIC_NAME_PATTERN.matcher(name).matches(),
-        "metric name must match %s",
+        "invalid metric name '%s': must match pattern '%s'",
+        name,
         METRIC_NAME_PATTERN.pattern());
   }