Bug 28998: (QA follow-up) Improve output on error

Bug 28998: (QA follow-up) Improve output on error

This patch updates the output_and_exit call to instead pass an error
parameter in the template and use it to display the warning instead of
the rest of the page content in the 'Manage two-factor authentication'
page.

This allows for translation and makes the page adhere to normal
practices.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>