Fix Issue #1461: TestNG not getting garbage collected

[juherr]

Fixes #1461.
Closes #1468

Did you remember to?

• Add test case(s)
• Update CHANGES.txt

All the work comes from @kiru in #1468

[ben-manes]

You might prefer using Guava testlib's GcFinalization, which has similar but more robust GC logic. Presumably the tests can have the dependency.

[kiru]

@ben-manes This is interesting, I didn't know that class, thank you. I this case, guava is missing in the test dependencies ( which is ok ).