apt: Add stgraber.net PPA by default

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
sssd: Allow setting a workgroup

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
apt: Add stgraber.net PPA to unattended-upgrades

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>