drivers/heater: add logging and minor improvements

- new heater_status logging message
 - run continously at low rate until configured sensor is found
 - fix px4io fd bugs (fd open/close/ioctl must be same thread)

msg/CMakeLists.txt

@@ -68,6 +68,7 @@ set(msg_files
 	geofence_result.msg
 	gps_dump.msg
 	gps_inject_data.msg
+	heater_status.msg
 	home_position.msg
 	hover_thrust_estimate.msg
 	input_rc.msg
@@ -127,11 +128,11 @@ set(msg_files
 	sensor_selection.msg
 	sensors_status_imu.msg
 	system_power.msg
+	takeoff_status.msg
 	task_stack_info.msg
 	tecs_status.msg
 	telemetry_status.msg
 	test_motor.msg
-	takeoff_status.msg
 	timesync.msg
 	timesync_status.msg
 	trajectory_bezier.msg