Making hive tests run against different MR versions

After we build hive, we want to have the ability to run unit tests against specific hadoop versions. Currently, the classpath constructed has multiple hadoop jars, which makes compiling okay, but running non-deterministic.

An example is HIVE-3156, where running against 0.23 shows issues with a couple of tests (which should either be shimmed out, or separated into directories the way it's done in the shims/ directory) - It would also be nice to find these issues out at test-compile time itself, rather than having them fail at test runtime.