add canonical_host param to web_app lwrp

added canonical_host param to web_app lwrp so that you can disable host redirection.

like this:

    web_app "my_site" do
      server_name node['hostname']
      server_aliases [node['fqdn'], "my-site.example.com"]
      docroot "/srv/www/my_site"
      canonical_host false
    end