On Debian and Ubuntu, the default host-name field in dhclient.conf is
set to either "<hostname>" or "gethostname()" both of which get replaced
by the machine's hostname at query time.

The sed call currently present in lxc-clone hardcodes the hostname in
dhclient.conf, causing dpkg to prompt on isc-dhcp updates.
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>