message: action: don't assume default params in tests
  We should not assume that the firmware is already set to the default
  takeoff altitude because it might have been changed in the past.
diff: using namespace dronecode_sdk;
  -static void takeoff_and_hover_at_altitude(float altitude_m = NAN);
  +static void takeoff_and_hover_at_altitude(float altitude_m);
  TEST_F(SitlTest, ActionHoverSyncDefault)
  {
  - takeoff_and_hover_at_altitude();
  + takeoff_and_hover_at_altitude(2.5);
  }
  TEST_F(SitlTest, ActionHoverSyncHigher)
  @@ -51,12 +51,6 @@ void takeoff_and_hover_at_altitude(float altitude_m)
  EXPECT_EQ(action_ret, ActionResult::SUCCESS);
  std::this_thread::sleep_for(std::chrono::seconds(1));
  - if (std::isfinite(altitude_m)) {
  - action->set_takeoff_altitude(altitude_m);
  - } else {
  - // The default should be 2.5 m, so we check against that.
  - altitude_m = 2.5f;
  - }
  action_ret = action->takeoff();
  EXPECT_EQ(action_ret, ActionResult::SUCCESS);
  