Replace usages RandomizedTestingTask with built-in Gradle Test (#40564)

This commit replaces the existing RandomizedTestingTask and supporting code with Gradle's built-in JUnit support via the Test task type. Additionally, the previous workaround to disable all tasks named "test" and create new unit testing tasks named "unitTest" has been removed such that the "test" task now runs unit tests as per the normal Gradle Java plugin conventions

benchmarks/build.gradle

@@ -24,7 +24,7 @@ mainClassName = 'org.openjdk.jmh.Main'
 assemble.enabled = false
 archivesBaseName = 'elasticsearch-benchmarks'
 
-unitTest.enabled = false
+test.enabled = false
 
 dependencies {
     compile("org.elasticsearch:elasticsearch:${version}") {

buildSrc/build.gradle

@@ -199,24 +199,21 @@ if (project != rootProject) {
     into localDownloads
   }
 
-  unitTest {
+  test {
     // The test task is configured to runtimeJava version, but build-tools doesn't support all of them, so test
     // with compiler instead on the ones that are too old.
     if (project.runtimeJavaVersion <= JavaVersion.VERSION_1_10) {
-      jvm = "${project.compilerJavaHome}/bin/java"
+      executable = "${project.compilerJavaHome}/bin/java"
     }
   }
-
-  // This can't be an RandomizedTestingTask because we can't yet reference it
+
   task integTest(type: Test) {
     // integration test requires the local testing repo for example plugin builds
     dependsOn project.rootProject.allprojects.collect {
       it.tasks.matching { it.name == 'publishNebulaPublicationToLocalTestRepository'}
     }
     dependsOn setupLocalDownloads
     exclude "**/*Tests.class"
-    testClassesDirs = sourceSets.test.output.classesDirs
-    classpath = sourceSets.test.runtimeClasspath
     inputs.dir(file("src/testKit"))
     // tell BuildExamplePluginsIT where to find the example plugins
     systemProperty (
@@ -232,11 +229,7 @@ if (project != rootProject) {
     if (isLuceneSnapshot) {
       systemProperty 'test.lucene-snapshot-revision', isLuceneSnapshot[0][1]
     }
-    String defaultParallel = System.getProperty('tests.jvms', project.rootProject.ext.defaultParallel)
-    if (defaultParallel == "auto") {
-        defaultParallel = Math.max(Runtime.getRuntime().availableProcessors(), 4)
-    }
-    maxParallelForks defaultParallel as Integer
+    maxParallelForks System.getProperty('tests.jvms', project.rootProject.ext.defaultParallel.toString()) as Integer
   }
   check.dependsOn(integTest)