Test USB Com port communication

[stenbergd]

Now that the USB COM port communication is almost in place, it should be tested. Some test cases:

• Test data transmission using a FIFO buffer
• Test data transmission using a data array/buffer
• Test with and without mutex protection on buffers
• Test FIFO wrap-around
• Test maxing data capacity in buffers
• Test entering too much data in to buffers (send and receive)
• Test the command line interface (CLI)
• test sending gibberish to the CLI

[stenbergd]

All these things tested and work well. Only issue is that a deadlock can occur if TX queue becomes full, but there is a separate issue for that.