Create a unit test that checks the YARN Unmanaged AM API

We have several questions regarding the Unmanaged AM mode in YARN, and we need to ask some questions to the Hadoop team. To that end, we need to have a few code examples that check the parts of the API in question. That code must be part of REEF so we can run it automatically, yet have as few REEF dependencies as possible, so we can send it to other teams