Send the client hostname to be used if unset

[jeffmccune]

Without this patch the hostname is not being set based on the DHCP
offer. This is using a relatively stock Debian Squeeze installation.
The hostname has been cleared from /etc/hostname

This patch requires an accompanying change to dhclient on the agent.
The following exit hook will properly set the hostname on Squeeze.

# /etc/dhcp/dhclient-exit-hooks.d/hostname
export PATH=/opt/puppet/bin:/usr/bin:/bin:/sbin:/usr/sbin:$PATH
hostname $new_host_name
puppet resource host $(facter fqdn) \
  ensure=present \
  ip=$(facter ipaddress) \
  host_aliases=$(facter hostname)