Major Description
When YARN 2.1.0-beta (non-RC) is released, we should upgrade Samza to it. This includes updating hello-samza, as well. We should also remove the classifier builds in the build.gradle, which allowed for building Samza with multiple versions of YARN. Based on SAMZA-5 discussion, it sounds like 2.1.0-beta+ should remain API-compatible, so we should just use that API (and the latest YARN version) for samza-yarn dependencies.