Mount cgroup filesystem only on Debian Wheezy

Ubuntu, and probably Debian Jessie use systemd to manage cgroups, so
manual mounting on these systems is not required.
Add option to upgrade newly created containers

New LXC containers created using 'lxc-ginas' script will be
automatically upgraded using security.debian.org repository, so at the
first start they should be more secure. This makes new container
creation time a little longer, so it can be optionally disabled using
a variable.
Change list of default packages in LXC containers
FIx a typo in 'lxc' role
Change list of installed LXC packages on Ubuntu

Ubuntu 14.04 needs an updated libcgmanager0 package for LXC to work
correctly.
Merge pull request #103 from drybjed/lxc-fixes

Various fixes and enhancements to 'lxc' role