Incorrect hadoop-yarn-registry version

In the root pom we define hadoop.version and use this for several hadoop artifacts. The version is not defined for hadoop-yarn-registry so if we compile Oozie with -Dhive.version=2.1.0 -Dhadoop.version=2.8.5 most of the hadoop jars will use version 2.8.5, but hadoop-yarn-registry will use version 2.7.1 Let's harmonize this.