PROTON-224: Arrange for proton_test to treat ProtonUnsupportedOperationException (the exception used by the Java stacks to signal an unimplemented Proton feature) automatically as a skipped test

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1443914 13f79535-47bb-0310-9956-ffa450edef68