Switch to debug with server=n (#48188)

Before this change one needed to re-start debugging several times, as we
launched multiple JVMs in debug mode.
With this option the IDE has the option to re-launch and listen for
connections again leading for to a more pleasant experience.

TESTING.asciidoc

@@ -43,6 +43,12 @@ supports a remote debugging option:
 ./gradlew run --debug-jvm
 ---------------------------------------------------------------------------
 
+This will instruct all JVMs (including any that run cli tools such as creating the keyring or adding users)
+to suspend and initiate a debug connection on port incrementing from  5005.
+As such the IDE needs to be instructed to listen for connections on this port.
+Since we might run multiple JVMs as part of configuring and starting the cluster it's
+recommended to have the option to aut restart checked.
+
 ==== Distribution
 
 By default a node is started with the zip distribution.

buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/RunTask.java

@@ -36,7 +36,7 @@ public Boolean getDebug() {
 
     @Override
     public void beforeStart() {
-        int debugPort = 8000;
+        int debugPort = 5005;
         int httpPort = 9200;
         int transportPort = 9300;
         Map<String, String> additionalSettings = System.getProperties().entrySet().stream()
@@ -57,7 +57,7 @@ public void beforeStart() {
                         "Running elasticsearch in debug mode, {} suspending until connected on debugPort {}",
                         node, debugPort
                     );
-                    node.jvmArgs("-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=" + debugPort);
+                    node.jvmArgs("-agentlib:jdwp=transport=dt_socket,server=n,suspend=y,address=" + debugPort);
                     debugPort += 1;
                 }
             }