add lock to keyboard demo

c_os/user/demo/KeyboardDemo.cc

@@ -16,10 +16,17 @@ void KeyboardDemo::run() {
 
     kout << "Keyboard Demo: " << endl;
 
+    kout.lock();
+    kout.clear();
+    kout << "Info: Die Keyboard Demo sperrt den Output Stream:\n"
+         << "      Wenn die Preemption Demo laeuft wird diese also erst\n"
+         << "      fortfahren wenn die Keyboard Demo wieder beendet ist." << endl;
+
     while (true) {
         kout << listener.waitForKeyEvent();
         kout.flush();
     }
 
+    kout.unlock();
     scheduler.exit();
 }

c_os/user/demo/KeyboardDemo.h

@@ -31,6 +31,7 @@ public:
     ~KeyboardDemo() override {
         log << INFO << "Uninitialized KeyboardDemo" << endl;
         kevman.unsubscribe(this->listener);
+        kout.unlock();
     }
 
     void run() override;