[COOK-3531] Use hostname as default instance name
[COOK-3531] Use hostname as default instance name

Signed-off-by: Seth Vargo <81550dbf04dfd8537ff7b3c014c6fbf86e0889dc@gmail.com>

gsreynolds/varnish,KierranM/varnish,rackspace-cookbooks/varnish,gsreynolds/varnish,GannettDigital/chef-varnish,gusrc/varnish,bitzesty/varnish,TAKEALOT/varnish,yoshiwaan/varnish,elastera/varnish,gusrc/varnish,KierranM/varnish,yoshiwaan/varnish,gusrc/varnish,NREL-cookbooks/varnish,rackspace-cookbooks/varnish,elastera/varnish,rackspace-cookbooks/varnish,GannettDigital/chef-varnish,jujugrrr/varnish,TAKEALOT/varnish,NREL-cookbooks/varnish,jujugrrr/varnish