Migration to TestNG and parallelization of unit tests

[chrisengelsma]

This PR migrates the underlying test package from JUnit to TestNG. The reason for this migration are as follows:

1. TestNG provides much better granularity when it comes to defining specific test method behavior
2. Much less markup
3. Parallel testing support. The number of testing threads currently set in this PR is set to 5 threads.

Documentation on TestNG can be found here: http://testng.org/doc/documentation-main.html