[PATCH 2/3] settings: Also define SERVER_EMAIL for email logs

[Finucane, Stephen]

> Django can send emails to admins on 500 HTTP errors when DEBUG is false.
> That looks handy. That mechanism uses SERVER_EMAIL for the From:
> address, which defaults to root at localhost and can cause problems in the
> email delivery.
> 
> Use the same address than DEFAULT_FROM_EMAIL by default.
> 
> Signed-off-by: Damien Lespiau <damien.lespiau at intel.com>

Acked-by: Stephen Finucane <stephen.finucane at intel.com>