command socket: use hash if needed

command socket: use hash if needed

The container command socket is an abstract unix socket containing
the lxcpath and container name.  Those can be too long.  In that case,
use the hash of the lxcpath and lxcname.  Continue to use the path and
name if possible to avoid any back compat issues.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>