lxc-test-{unpriv,usernic.in}: make sure to chgrp as well

These tests are failing on new kernels because the container root is
not privileged over the directories, since privilege no requires
the group being mapped into the container.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Remove mention of mountcgroups in ubuntu.common config

That mount hook predates the lxc.mount.auto = cgroup option.  So mention
that instead.

Perhaps we should simply drop the mountcgroup hook from the tree, but
I'm not doing that in this patch.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>