Change revision string to be the package version.

Currently the revision that is returned contains not only the package version but also the package title (id). That is not necessary and causes unpleasant side effects - i.e. when the revision is displayed in the pipeline history (http://serveurl:port/go/tab/pipeline/history/pipeline-namw) it displays the package name (if it's long even only parts of it) and truncates the real version.