Land drone safely

- improved landing
- navigate to the return point defined in JSON file
- land drone safely without timeouts

Issue: https://denyspopov.atlassian.net/browse/AZ-24
Type: New Feature

src/az_drone_controller.cpp

@@ -168,20 +168,13 @@ bool AzDroneController::stateFlyMission(void)
 
 void AzDroneController::missionFinishedSlot(void)
 {
-    qDebug() << "AzDroneController::missionFinishedSlot() Landing the drone.";
-    // TODO!! Check return value and print warnings and errors.
-    mAction->land();
-    // TODO!! This must be improved a lot. Disarming should be done when drone lands.
-    QTimer::singleShot(20000, this, &AzDroneController::disarmDroneSlot);
-}
+    // TODO!! Maybe use Telemetry::subscribe_landed_state() later to get the state of the landing.
+    qDebug() << "AzDroneController::missionFinishedSlot() Mission finished. Landing the drone.";
+    Action::Result result = mAction->land();
 
-void AzDroneController::disarmDroneSlot(void)
-{
-    qDebug() << "AzDroneController::disarmDroneSlot() Disarming the drone and quit.";
-    // TODO!! Check return value and print warnings and errors.
-    mAction->disarm();
-    // TODO!! Check with the team what to do after the landing.
-    QCoreApplication::instance()->quit();
+    if (result != Action::Result::Success) {
+        std::cerr << "mAction->land() failed. Reason: " << result << endl;
+    }
 }
 
 void AzDroneController::droneStateMachineSlot(void)