[Backport] Replace usages RandomizedTestingTask with built-in Gradle Test (#40978)

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

@@ -199,11 +199,11 @@ 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"
     }
   }
 
@@ -215,8 +215,6 @@ if (project != rootProject) {
     }
     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 +230,7 @@ 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)