Enable to ignore fatal errors

[pazeshun]

When a Dynamixel motor detects some dangerous situations, the motor goes torque off:
https://emanual.robotis.com/docs/en/dxl/mx/mx-28/#shutdown
However, we sometimes want the motor to ignore the error and continue working.
For example, when we use the motor in robotic fingers and these fingers grasp an object, these fingers should continue exerting strong force not to drop the object.
In that situation, the motor continues detecting a big load, easily goes into Overload Error, and torque off.

To avoid this problem, we can remove errors from Shutdown (and Alarm LED) register of the motor to prevent torque off due to these errors.
However, even when we do that, these errors are included in every response from the motor.
dynamixel_motor detects them and prints many error messages (especially when Overload Error):

dynamixel_motor/dynamixel_driver/src/dynamixel_driver/dynamixel_io.py

Lines 985 to 1005 in 3d84232

	if not error_code & DXL_OVERHEATING_ERROR == 0:
	msg = 'Overheating Error ' + ex_message
	exception = FatalErrorCodeError(msg, error_code)
	if not error_code & DXL_OVERLOAD_ERROR == 0:
	msg = 'Overload Error ' + ex_message
	exception = FatalErrorCodeError(msg, error_code)
	if not error_code & DXL_INPUT_VOLTAGE_ERROR == 0:
	msg = 'Input Voltage Error ' + ex_message
	exception = NonfatalErrorCodeError(msg, error_code)
	if not error_code & DXL_ANGLE_LIMIT_ERROR == 0:
	msg = 'Angle Limit Error ' + ex_message
	exception = NonfatalErrorCodeError(msg, error_code)
	if not error_code & DXL_RANGE_ERROR == 0:
	msg = 'Range Error ' + ex_message
	exception = NonfatalErrorCodeError(msg, error_code)
	if not error_code & DXL_CHECKSUM_ERROR == 0:
	msg = 'Checksum Error ' + ex_message
	exception = NonfatalErrorCodeError(msg, error_code)
	if not error_code & DXL_INSTRUCTION_ERROR == 0:
	msg = 'Instruction Error ' + ex_message
	exception = NonfatalErrorCodeError(msg, error_code)

dynamixel_motor/dynamixel_driver/src/dynamixel_driver/dynamixel_serial_proxy.py

Lines 228 to 238 in 3d84232

	except dynamixel_io.FatalErrorCodeError, fece:
	rospy.logerr(fece)
	except dynamixel_io.NonfatalErrorCodeError, nfece:
	self.error_counts['non_fatal'] += 1
	rospy.logdebug(nfece)
	except dynamixel_io.ChecksumError, cse:
	self.error_counts['checksum'] += 1
	rospy.logdebug(cse)
	except dynamixel_io.DroppedPacketError, dpe:
	self.error_counts['dropped'] += 1
	rospy.logdebug(dpe.message)

This PR enables to suppress that phenomenon by setting rosparam.