respect locale preferences on new user account confirmation failure page

fixes CAT-464

Test Plan
  1. Fire up canvas with full i18n support configured
     (i.e. $ RAILS_LOAD_ALL_LOCALES=true rails server)
  2. Submit a POST request to the canvas api to create a new user
     (i.e. '/accounts/:id/users') with request headers [:user][:locale]
     set to a supported canvas locale (i.e. 'zh')
  3. Navigate to the new user account confirmation page from the email
     link, set a password and submit the form
  4. With your new user still signed in, navigate back to the confirm URL
     and ensure the page is still localized
  5. Logout from canvas and navigate back to the confirm URL again and
     ensure the page is still localized

Change-Id: I47127098f88b53d9b66b2a739cc4fd8836f14523
Reviewed-on: https://gerrit.instructure.com/39661
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ethan Gunderson <egunderson@instructure.com>
Reviewed-by: Nick Houle <nhoule@instructure.com>
Product-Review: Dave Donahue <ddonahue@instructure.com>
QA-Review: Dave Donahue <ddonahue@instructure.com>