Add module unit-tests-guava-testlib.

[motlin]

This is an experiment to run Guava's testlib tests on Eclipse Collections containers. I started with just maps, and this test suite is based on https://github.com/google/guava/blob/master/guava-testlib/src/com/google/common/collect/testing/TestsForMapsInJavaUtil.java.

A few tests fail, just on compute() and merge() methods, and just on edge cases involving replacing nulls.