Merge pull request #776 from efryntov/fix/feedback-missing-shutdown

Android: shut down feedback executors before awaiting termination

MobileLibrary/Android/PsiphonTunnel/PsiphonTunnel.java

@@ -319,6 +319,7 @@ public class PsiphonTunnel {
         private final ExecutorService callbackQueue = Executors.newSingleThreadExecutor();
 
         void shutdownAndAwaitTermination(ExecutorService pool) {
+            pool.shutdown();
             try {
                 // Wait a while for existing tasks to terminate
                 if (!pool.awaitTermination(5, TimeUnit.SECONDS)) {