Do not print null method name in reproduce line (elastic#41691)

This commit updates the reproduce line that is printed out when a test
fails so that it does not output `.null` as the method name when the
failure is not a specific method but a class level issue such as
threads being leaked from the SUITE. Previously, when this occurred the
reproduce line would look like:

`./gradlew :server:integTest --tests "org.elasticsearch.indices.memory.breaker.CircuitBreakerServiceIT.null"`

and after this change, the line no longer contains the `.null` after
the class name.

test/framework/src/main/java/org/elasticsearch/test/junit/listeners/ReproduceInfoPrinter.java

@@ -82,8 +82,11 @@ public void testFailure(Failure failure) throws Exception {
         b.append(task);
         b.append(" --tests \"");
         b.append(failure.getDescription().getClassName());
-        b.append(".");
-        b.append(failure.getDescription().getMethodName());
+        final String methodName = failure.getDescription().getMethodName();
+        if (methodName != null) {
+            b.append(".");
+            b.append(failure.getDescription().getMethodName());
+        }
         b.append("\"");
 
         GradleMessageBuilder gradleMessageBuilder = new GradleMessageBuilder(b);