OOZIE-1166 Print a more helpful message when ProxyUserService is configured wrong (rkanter)

git-svn-id: https://svn.apache.org/repos/asf/oozie/trunk@1433796 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of github.com:griddynamics/oozie into trunk-gd