NetUtils testing

- Refactor tests:
  - Upgrade tests to use jUnit4
  - Add hamcrest dependency (contribution of by Laszio Hornyak)
  - Break big tests in small unit tests
  - Replace assertTrue/False with complex conditions by assertThat with
specific matchers
- Remove dead code:
  - Private static method never called locally
- Add test for method that validates cidrs

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>