PROTON-194: modify Maven set-up so that proton-j and proton-system-tests do not depend on top-level proton-project, thereby allowing these sub-projects to be independently checked out and built

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/branches/jni-binding@1434025 13f79535-47bb-0310-9956-ffa450edef68