Reporting errors in the dynamixel tools (& protocol 2)

[jbmouret]

When we run build/src/tools/p2-dynamixel -t 50 -p /dev/tty.ROBOTIS_210_40-SPPDev --id 1 --enable 1 torque-enable

We get:
An error (out_of_range from map::at: key not found) has been caught. You probably used a nonexistent ID.

But actually there is an error in the ping, that is not reported:
err message:Actuator with ID 1 reported the following error: Device alert, check Hardware Error field from Control Table;

Also, we should automatically check the control table to know what this is about.

[jbmouret]

This is similar to #36