Double-clickers are logging in twice because the form is submitted twice
and the server will handle both requests concurrently. This is not a big
issue but it becomes one when a user login in for the first time is a
double-clicker. Server will handle both requests concurrently resulting
in creating 2 accounts for the same user.
This change disables the form submission after the first submit.
Change-Id: Ida55e632618c72ab11e536854c654ed423a0f195
66a0c4a343