Need to add unit tests to jans-core

[jans-core](https://github.com/JanssenProject/jans-core) doesn't have unit tests for the most part. With significant size (20k lines of java) of code, the coverage is almost zero.

Since jans-core is used extensively across multiple jans modules, it is important to ensure integrity of this code with unit tests.

The reason for the non-existence of tests may be due to the fact that jans-core code was extracted out of existing well-tested modules and tests were not extracted for the same.