Replace usages RandomizedTestingTask with built-in Gradle Test (#40978) (#40995)

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.

(cherry picked from commit 323f312)

Author: mark-vieira

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 (
@@ -232,6 +230,7 @@ if (project != rootProject) {
     if (isLuceneSnapshot) {
       systemProperty 'test.lucene-snapshot-revision', isLuceneSnapshot[0][1]
     }
+    maxParallelForks System.getProperty('tests.jvms', project.rootProject.ext.defaultParallel.toString()) as Integer
   }
   check.dependsOn(integTest)