Trying to fix non-deterministic test

- not sure of a way other than putting Thread.sleep in here to give time after each CountDownLatch triggers for the process scheduler to execute the next line of each thread

See ReactiveX#201 for more information.

rxjava-core/src/main/java/rx/operators/OperationMerge.java

@@ -441,6 +441,15 @@ public void onNext(String v) {
             o1.onNextBeingSent.await();
             o2.onNextBeingSent.await();
 
+            // I can't think of a way to know for sure that both threads have or are trying to send onNext
+            // since I can't use a CountDownLatch for "after" onNext since I want to catch during it
+            // but I can't know for sure onNext is invoked
+            // so I'm unfortunately reverting to using a Thread.sleep to allow the process scheduler time
+            // to make sure after o1.onNextBeingSent and o2.onNextBeingSent are hit that the following
+            // onNext is invoked.
+
+            Thread.sleep(300);
+
             try { // in try/finally so threads are released via latch countDown even if assertion fails
                 assertEquals(1, concurrentCounter.get());
             } finally {
@@ -541,6 +550,8 @@ public Subscription subscribe(final Observer<String> observer) {
                     public void run() {
                         onNextBeingSent.countDown();
                         observer.onNext("hello");
+                        // I can't use a countDownLatch to prove we are actually sending 'onNext'
+                        // since it will block if synchronized and I'll deadlock
                         observer.onCompleted();
                     }