ubuntu: Make vim part of base template

This moves vim back to the default list of packages, drops the duplicate
ssh entry which means that unless extra packages are passed through
--packages, container creation won't invoke apt-get anymore.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>