Tests:
- Build deb and install in buster image. Manually remove backports
sources file. Security page does not show backports notice. Updates
page shows button to activate backports.
- Activate backports from updates page. Success message is shown and
button to activate backports is removed. Security page shows
backports notice.
Signed-off-by: James Valleroy <jvalleroy@mailbox.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>