site.yml: move validate task to it's own play

This needs to be in it's own play with ceph-defaults included
so that I can validate things that might be defaulted in that
role.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>

site.yml.sample

@@ -69,10 +69,32 @@
         - ansible_distribution == 'Fedora'
         - ansible_distribution_major_version|int >= 23
 
+- hosts:
+  - mons
+  - agents
+  - osds
+  - mdss
+  - rgws
+  - nfss
+  - restapis
+  - rbdmirrors
+  - clients
+  - mgrs
+  - iscsi-gws
+
+  gather_facts: false
+
+  roles:
+    - ceph-defaults
+
+  tasks:
     - name: validate vars
       validate:
         mode: permissive
 
+    - fail:
+        msg: "failing for testing"
+
 - hosts: mons
   gather_facts: false
   become: True