Improve use of MAVSDK::Telemetry

Print health information if Telemetry::health_all_ok() fails.

Type: Improvement
Issue: https://denyspopov.atlassian.net/browse/AZ-15

src/az_drone_controller.h

@@ -67,12 +67,19 @@ private slots:
     // Disarms the drone and exits the application. TODO!! Discuss quitting the application.
     void disarmDroneSlot(void);
 
+    // Gets Telemetry::Health information in prearming.
+    void newHealthInfoSlot(Telemetry::Health health);
+
 signals:
     // Signal is emitted when Ardupilot sends a new position from the
     // MAVSDK thread. Signal goes through the main event loop and is
     // captured in the main thread to avoid threading issues.
     void newPosition(Telemetry::Position);
 
+    // If Telemetry::health_all_ok() fails, then autopilot subscripes for the healt updates to
+    // see exactly what is wrong. This signal is emitted to catch updates in the main thread.
+    void newHealthInfo(Telemetry::Health);
+
 private:
     Mavsdk mMavsdk;
     AzDroneState mDroneState;