Wait until iframe is fully loaded before submitting form

Two issues fixed:
- Race condition: If the token was returned by the API before the
  load event of the iframe fired, the form was submitted to the
  default target (= current page) --> the result of the API request
  is displayed on the page instead of running in the background
  Now making sure the load event of the iframe fired before and
  the form target is set to the iframe
- The hash (#) as source of the iframe made the load event never
  fire in Mozilla Firefox 29. Using the the source that was used
  before I74bbb0d4fa.

Bug: 65406
Change-Id: If04206fa99312977aa06c4bd3dfd1f897d6ce7b7
Merge "Wait until iframe is fully loaded before submitting form"