lxc-setcap.in: Set path to lxc-init

In lxc-setcap the path to lxc-init wasn't set right, so that
a call to the script failed with an error. This patch sets
the path to the right directory.

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