Previously, heat would leave the context roles empty when loading the stored context. When signaling heat used the stored context (trust scoped token), and if the context did not have any roles, it failed. Consequently, the process failed with the error 'trustee has no delegated roles'. This fix addresses this issue by populating roles when loading the stored context. As a result, loading the auth ref, and populating the roles from the token will confirm that any RBAC performed on the context roles will work as expected, and that the stack update succeeds.