Add the ability to run REST integration tests with 1 allocated processor (elastic#89234)

This commit adds a new system property `tests.configure_test_clusters_with_one_processor`
that configures REST integration tests to run with 1 allocated processor, this should help finding possible
deadlocks (if any) when the Elasticsearch nodes have `node.processors` set to 1.

Author: fcofdez

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/InternalTestClustersPlugin.java

@@ -10,7 +10,9 @@
 
 import org.elasticsearch.gradle.VersionProperties;
 import org.elasticsearch.gradle.internal.info.BuildParams;
+import org.elasticsearch.gradle.testclusters.ElasticsearchCluster;
 import org.elasticsearch.gradle.testclusters.TestClustersPlugin;
+import org.gradle.api.NamedDomainObjectContainer;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.provider.ProviderFactory;
@@ -36,6 +38,16 @@ public void apply(Project project) {
             version -> (version.equals(VersionProperties.getElasticsearchVersion()) && BuildParams.isSnapshotBuild() == false)
                 || BuildParams.getBwcVersions().unreleasedInfo(version) == null
         );
+
+        if (shouldConfigureTestClustersWithOneProcessor()) {
+            NamedDomainObjectContainer<ElasticsearchCluster> testClusters = (NamedDomainObjectContainer<ElasticsearchCluster>) project
+                .getExtensions()
+                .getByName(TestClustersPlugin.EXTENSION_NAME);
+            testClusters.configureEach(elasticsearchCluster -> elasticsearchCluster.setting("node.processors", "1"));
+        }
     }
 
+    private boolean shouldConfigureTestClustersWithOneProcessor() {
+        return Boolean.parseBoolean(System.getProperty("tests.configure_test_clusters_with_one_processor", "false"));
+    }
 }

test/framework/src/main/java/org/elasticsearch/test/InternalTestCluster.java

@@ -524,7 +524,7 @@ private static Settings getRandomNodeSettings(long seed) {
 
         builder.put(
             EsExecutors.NODE_PROCESSORS_SETTING.getKey(),
-            1 + random.nextInt(Math.min(4, Runtime.getRuntime().availableProcessors()))
+            RandomNumbers.randomIntBetween(random, 1, Math.min(4, Runtime.getRuntime().availableProcessors()))
         );
         if (random.nextBoolean()) {
             if (random.nextBoolean()) {