Don't join worker instances but hard stop them

src/anbox/runtime.cpp

@@ -77,8 +77,7 @@ void Runtime::stop() {
     service_.stop();
 
     for (auto& worker : workers_)
-        if (worker.joinable())
-            worker.join();
+        pthread_kill(worker.native_handle(), SIGTERM);
 }
 
 std::function<void(std::function<void()>)> Runtime::to_dispatcher_functional()

src/anbox/runtime.h

@@ -48,8 +48,7 @@ public:
     // the size configured at creation time.
     void start();
 
-    // stop cleanly shuts down a Runtime instance,
-    // joining all worker threads.
+    // stop cleanly shuts down a Runtime instance.
     void stop();
 
     // to_dispatcher_functional returns a function for integration