MAVSDK tests: Add minimal plane example

This will add coverage for baseline plane controllers.

test/mavsdk_tests/test_mission_plane.cpp

@@ -0,0 +1,24 @@
+//
+// Multicopter mission test.
+//
+// Author: Julian Oes <julian@oes.ch>
+
+#include <mavsdk/mavsdk.h>
+#include <mavsdk/plugins/action/action.h>
+#include <mavsdk/plugins/telemetry/telemetry.h>
+#include <iostream>
+#include <string>
+#include "autopilot_tester.h"
+
+
+TEST_CASE("Takeoff and land (Plane)", "[plane]")
+{
+    AutopilotTester tester;
+    tester.connect(connection_url);
+    tester.wait_until_ready();
+    tester.arm();
+    tester.takeoff();
+    tester.wait_until_hovering();
+    tester.land();
+    tester.wait_until_disarmed();
+}