Expose pid in new test clusters (elastic#97590)

Sometimes it is necessary for an integ test to poke at the Java process
of Elasticsearch. This commit makes a node's pid available through
ClusterHandle.

Author: rjernst

test/test-clusters/src/main/java/org/elasticsearch/test/cluster/ClusterHandle.java

@@ -71,6 +71,11 @@ public interface ClusterHandle extends Closeable {
      */
     String getName(int index);
 
+    /**
+     * Get the pid of the node for the given index.
+     */
+    long getPid(int index);
+
     /**
      * Returns a comma-separated list of TCP transport endpoints for cluster. If this method is called on an unstarted cluster, the cluster
      * will be started. This method is thread-safe and subsequent calls will wait for cluster start and availability.

test/test-clusters/src/main/java/org/elasticsearch/test/cluster/DefaultElasticsearchCluster.java

@@ -95,6 +95,12 @@ public String getName(int index) {
         return handle.getName(index);
     }
 
+    @Override
+    public long getPid(int index) {
+        checkHandle();
+        return handle.getPid(index);
+    }
+
     @Override
     public String getTransportEndpoints() {
         checkHandle();

test/test-clusters/src/main/java/org/elasticsearch/test/cluster/local/LocalClusterFactory.java

@@ -222,6 +222,13 @@ public String getName() {
             return name;
         }
 
+        public long getPid() {
+            if (process == null) {
+                throw new IllegalStateException("Process has not been started, cannot get pid");
+            }
+            return process.pid();
+        }
+
         public LocalNodeSpec getSpec() {
             return spec;
         }

test/test-clusters/src/main/java/org/elasticsearch/test/cluster/local/LocalClusterHandle.java

@@ -160,6 +160,11 @@ public String getName(int index) {
         return nodes.get(index).getName();
     }
 
+    @Override
+    public long getPid(int index) {
+        return nodes.get(index).getPid();
+    }
+
     public void stopNode(int index) {
         nodes.get(index).stop(false);
     }