Add support for running unit tests in build-scripts

Allow to disable tests in build-profile to enable running them in other modules when PERL5LIB is defined.

Alternative to #27.

Unit tests and other mods provided by #27 included and unit tests working successfully. To run them, the following command must be used:
```bash
mvn -pl build-scripts test
```

It is also possible to use the `mvn` command documented in `BUILD_INFO` to rebuild/test everything (build tools are a bit specific and require some specific Maven options to be built successfully).
This is a very good approach for validating the test infrastructure, BTW.