new fact to check if dhcp is used;

from https://github.com/gds-operations/puppet-resolvconf/blob/master/lib/facter/dhcp_enabled.rb
configure dhclient if its used in /e/network/interfaces

we don't dhclient to to set domain and search in /etc/reslov.conf
bigcouch has a strange way to find its hostname. It uses the domain
stanza in /etc/resolv.conf to find its domain