ubuntu template: use -updates and -security (v3)

ubuntu template: use -updates and -security (v3)

Particularly for LTS releases, which many people will want to use in
their containers, it is not wise to not use release-security and
release-updates.  Furthermore the fix allowing ssh to allow the container
to shut down is in lucid-updates only.

With this patch, after debootstrapping a container, we add -updates and
-security to sources.list and do an upgrade under chroot.  Unfortunately
we need to do this because debootstrap doesn't know how to.

Changelog:
	Nov 14: as Stéphane Graber suggested, make sure no daemons start on
		the host while doing dist-upgrade from chroot.
	Nov 15: use security.ubuntu.com, not mirror. (stgraber)

Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>