PROTON-341: Update the Ruby interop tests.

Added a new helper function to Data to return an instance of Described.

Added new helper methods to the interop.rb file for testing Arrays.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1495479 13f79535-47bb-0310-9956-ffa450edef68