Updating SerailizationTestUtils to make it generic.

[LavishKothari]

Issue#631

This PR cleans the code related to serailization tests.

• Specifically making SerailizationTestUtils#serializeAndDeserialize generic instead of dealing with raw Object.
• Removing unnecessary @SuppressWarnings("unchecked")
• minor cleaning in the tests.

---

• I read and understood https://github.com/jgrapht/jgrapht/wiki/Become-a-Contributor
• I read and understood https://github.com/jgrapht/jgrapht/wiki/How-to-make-your-first-%28code%29-contribution
• I added unit tests - Unit tests are not required for this PR
• I added documentation
• I followed the Coding and Style Conventions
• I have not modified HISTORY.md or CONTRIBUTORS.md
• I ensured that the git commit message is a good one

[jsichi]

Nice!