Issue vagrant-landrush#176 Create no reverse DNS entry for CNAME entries

lib/landrush/action/setup.rb

@@ -69,11 +69,19 @@ def setup_static_dns
           unless Store.hosts.has?(hostname, dns_value)
             info "adding static entry: #{hostname} => #{dns_value}"
             Store.hosts.set hostname, dns_value
-            Store.hosts.set(IPAddr.new(dns_value).reverse, hostname)
+            unless static_dns_ip_address(dns_value).nil?
+              Store.hosts.set(IPAddr.new(dns_value).reverse, hostname)
+            end
           end
         end
       end
 
+      def static_dns_ip_address(dns_value)
+        return IPAddr.new(dns_value)
+      rescue StandardError
+        return nil
+      end
+
       def record_machine_dns_entry
         ip_address = machine.config.landrush.host_ip_address || host_ip_address