fix(parallel): uses InheritableThreadLocal for TestNG test runner (#205)

This improves scenarios of parallel execution with TestNG and other Arquillian extensions such as Cube.

It does not fix arquillian/arquillian-extension-drone#87 yet.

Author: SarahFaller213

testng/core/src/main/java/org/jboss/arquillian/testng/Arquillian.java

@@ -49,8 +49,8 @@
 @Listeners(Arquillian.UpdateResultListener.class)
 public abstract class Arquillian implements IHookable {
     public static final String ARQUILLIAN_DATA_PROVIDER = "ARQUILLIAN_DATA_PROVIDER";
-    private static ThreadLocal<TestRunnerAdaptor> deployableTest = new ThreadLocal<TestRunnerAdaptor>();
-    private static ThreadLocal<Stack<Cycle>> cycleStack = new ThreadLocal<Stack<Cycle>>() {
+    private static InheritableThreadLocal<TestRunnerAdaptor> deployableTest = new InheritableThreadLocal<TestRunnerAdaptor>();
+    private static InheritableThreadLocal<Stack<Cycle>> cycleStack = new InheritableThreadLocal<Stack<Cycle>>() {
         protected java.util.Stack<Cycle> initialValue() {
             return new Stack<Cycle>();
         }