Tools: autotest: fix for Plane receiver health test

Won't be healthy until SITL is repolled for RC input

Tools/autotest/arduplane.py

@@ -814,6 +814,8 @@ class AutoTestPlane(AutoTest):
 #            raise NotAchievedException("Sensor healthy when it shouldn't be")
         self.set_parameter("SIM_RC_FAIL", 0)
         self.drain_mav_unparsed()
+        # have to allow time for RC to be fetched from SITL
+        self.delay_sim_time(0.5)
         m = self.mav.recv_match(type='SYS_STATUS', blocking=True)
         self.progress("Testing receiver enabled")
         if (not (m.onboard_control_sensors_enabled & receiver_bit)):