Use validate_legacy

This changes all the puppet 3 validate_* functions
to use the validate_legacy function.

The validate_legacy function has been available since
about three years but require Puppet >= 4.4.0 and since
there is Puppet 4.10.12 as latest we should assume people
are running a fairly new Puppet 4 version.

This is the first step to then remove all validate function
calls and use proper types for parameter as described in spec [1].

[1] https://review.openstack.org/#/c/568929/

Change-Id: Id8a8be3f4e8d7f6f69371bd2df29e1b5bec90fb4

manifests/controller.pp

@@ -54,12 +54,13 @@ class ovn::controller(
   $enable_hw_offload         = false,
   $mac_table_size            = 50000,
 ) {
+
   include ::ovn::params
   include ::vswitch::ovs
   include ::stdlib
 
-  validate_string($ovn_remote)
-  validate_string($ovn_encap_ip)
+  validate_legacy(String, 'validate_string', $ovn_remote)
+  validate_legacy(String, 'validate_string', $ovn_encap_ip)
 
   service { 'controller':
     ensure    => true,