fix(client): Fix the "Sign in" link on `/confirm_reset_password` if the user is in the force auth flow.

* The user should be returned to /force_auth instead of /sign_in

fixes #926
Merge pull request #1066 from mozilla/issue-926-sign-in-link-force-auth

fix(client): Fix the "Sign in" link on `/confirm_reset_password` if the user is in the force auth flow.