lxc-ubuntu: Remove trim option

Container trimming is a bad idea in general, Ubuntu since 12.04 allows
standard systems to run in containers and we've got separate code to
deal with 10.04, so let's just drop trim.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
call lxc_container_put when appropriate

Signed-off-by: S.Çağlar Onur <caglar@10ur.org>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>