If the user is not an admin, keep the existing admin_active settings
If the user is not an admin, keep the existing admin_active settings

Boolean in html are processed in such a way that: present=1 and absent=0
so by hiding the admin_active box to non-admins, we are sending an 'absent'
signal and thus if we do not handle this, we end-up with changing
involuntarily the admin_active flag.

pombredanne/mirrormanager2,pombredanne/mirrormanager2,pombredanne/mirrormanager2,pombredanne/mirrormanager2