CLOUD-2317 (Andy) : Create new pogo plug function to compose and return ...

...a URL to use in order to sign out of HP connected and return to a sign out URL belonging to the caller.  Included spec to validate the URL composition based on the latest URL pattern provided to us by HP.
If you know of a way to get 'to_query' to work within a spec, or if we really don't care about a spec for this, then I can refactor to remove duplication.