AP_InertialSensor: Use return value of blocking_read to handle calibration timeouts

When the ground station requests an Inertial sensor calibration, if it does not respond with a CMD_ACK in 30 seconds the blocking_read times out and continues the next calibration step regardless of if the user wants to continue. Since there is no way to cancel an in-progress calibration, this pull changes it to fail calibration on a timeout.