message: Takeoff land example: Wait until vehicle is ready
  Currently, takeoff-land example exits if vehicle is not ready for
  arming. It should rather rather wait until vehicle is ready.
diff: #include <thread>
  using namespace dronecore;
  +using namespace std::this_thread;
  +using namespace std::chrono;
  #define ERROR_CONSOLE_TEXT "\033[31m" //Turn text on console red
  #define TELEMETRY_CONSOLE_TEXT "\033[34m" //Turn text on console blue
  @@ -48,7 +50,7 @@ int main(int argc, char **argv)
  });
  // We usually receive heartbeats at 1Hz, therefore we should find a device after around 2 seconds.
  - std::this_thread::sleep_for(std::chrono::seconds(2));
  + sleep_for(seconds(2));
  if (!discovered_device) {
  std::cout << ERROR_CONSOLE_TEXT << "No device found, exiting." << NORMAL_CONSOLE_TEXT << std::endl;
  @@ -82,9 +84,9 @@ int main(int argc, char **argv)
  // Check if vehicle is ready to arm
  - if (telemetry->health_all_ok() != true) {
  - std::cout << ERROR_CONSOLE_TEXT << "Vehicle not ready to arm" << NORMAL_CONSOLE_TEXT << std::endl;
  - return 1;
  + while (telemetry->health_all_ok() != true) {
  + std::cout << "Vehicle is getting ready to arm" << std::endl;
  + sleep_for(seconds(1));
  }
  // Arm vehicle
  @@ -107,7 +109,7 @@ int main(int argc, char **argv)
  }
  // Let it hover for a bit before landing again.
  - std::this_thread::sleep_for(std::chrono::seconds(10));
  + sleep_for(seconds(10));
  std::cout << "Landing..." << std::endl;
  const Action::Result land_result = action->land();
  @@ -118,7 +120,7 @@ int main(int argc, char **argv)
  }
  // We are relying on auto-disarming but let's keep watching the telemetry for a bit longer.
  - std::this_thread::sleep_for(std::chrono::seconds(5));
  + sleep_for(seconds(5));
  std::cout << "Finished..." << std::endl;
  return 0;
  }
  