Build: Add back support for tests.jvm.argline

closes #14541

buildSrc/src/main/groovy/com/carrotsearch/gradle/junit4/RandomizedTestingTask.groovy

@@ -61,6 +61,11 @@ class RandomizedTestingTask extends DefaultTask {
     ListenersConfiguration listenersConfig = new ListenersConfiguration(task: this)
 
     List<String> jvmArgs = new ArrayList<>()
+
+    @Optional
+    @Input
+    String argLine = null
+
     Map<String, String> systemProperties = new HashMap<>()
     PatternFilterable patternSet = new PatternSet()
 
@@ -193,6 +198,9 @@ class RandomizedTestingTask extends DefaultTask {
             for (String arg : jvmArgs) {
                 jvmarg(value: arg)
             }
+            if (argLine != null) {
+                jvmarg(line: argLine)
+            }
             fileset(dir: testClassesDir) {
                 for (String includePattern : patternSet.getIncludes()) {
                     include(name: includePattern)

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -111,6 +111,7 @@ class BuildPlugin implements Plugin<Project> {
             File heapdumpDir = new File(project.buildDir, 'heapdump')
             heapdumpDir.mkdirs()
             jvmArg '-XX:HeapDumpPath=' + heapdumpDir
+            argLine System.getProperty('tests.jvm.argline')
 
             // we use './temp' since this is per JVM and tests are forbidden from writing to CWD
             systemProperty 'java.io.tmpdir', './temp'