test: tcp needs improvements

[AndreasAakesson]

• The current README does not explain what the test does.

The tcp test works fine, but since tcp is very complex (a lot of special cases), a lot more has to be done and improved with the test.

On this issue I would like to take ideas for more cases to be tested. An example would be:

• Having N concurrent connections sending data.

This also needs work on the other end (clients connection to IncludeOS, created by python script).

Ideas and suggestions are appreciated.