Fix incomplete destruction of unprivileged ephemeral containers

Fix incomplete destruction of unprivileged ephemeral containers

If an unprivileged ephemeral container is started as follows,

    lxc-start-ephemeral -o trusty -n test_ephemeral

Then an empty directory remains upon exit from the container,

    ~/.local/share/lxc/test_ephemeral/tmpfs/delta0

(The tmpfs filesystem is successfully unmounted, but we seem to lack
permission to delete the delta0 directory).

This issue arose following commits 4799a1e and dd2271e .

The following patch resolves the issue. It has been tested on ubuntu
14.04 with the lxc-daily ppa.
Since gmail screws up the formatting of the patch via line-wrapping
etc, please copy the patch from the issue-tracker rather than from
this email.

Signed-off by: Oleg Freedholm <overlayfs@gmail.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>