driver: no tests for motoman-specific simple_message and IRC extensions

[gavanderhoorn]

The simple_message and industrial_robot_client packages have a number of tests to make sure the (de)serialisation and data structure classes work as they are supposed to. While the motoman_driver package has introduced a number of motoman-specific extensions to that infrastructure, it did not also introduce tests for them.

Based on our experience with the tests in simple_message, issues like #91 are examples of problems that would most likely have been uncovered by a solid test set.

This situation should be rectified and tests for at least the set of simple messages implemented in this package should be added.