Switch custom metric to cpu

Author: Bill Prin

monitoring/cloud-client/src/test/java/com/example/monitoring/SnippetsIT.java

@@ -77,7 +77,7 @@ public void testListTimeSeries() throws Exception {
     System.setProperty("projectId", SnippetsIT.getProjectId());
     Snippets snippets = new Snippets();
 
-    snippets.listTimeSeries("metric.type=\"custom.googleapis.com/my_metric\"");
+    snippets.listTimeSeries("metric.type=\"compute.googleapis.com/instance/cpu/utilization\"");
 
     // Assert
     String got = bout.toString();