WL-3611 Build a full Tool.HELPER_DONE_URL.

In Sakai 10 the Tool.HELPER_DONE_URL must be a full URL, rather than just a path, otherwise an exception gets thrown. This is a simpler fix than fixing the login tool although that should get done in the long run.
Merge pull request #138 from ox-it/WL-3611

WL-3611 Build a full Tool.HELPER_DONE_URL.