Make two workflows from 'validations' produce output

Now two 'list' workflows don't return the result. This commit adds
"output" section to both of them.

Change-Id: Ide857991b570593a6e6b93097171edadf51e4fcd
Close-bug: #1761504
Related-bug: #1759417

workbooks/validations.yaml

@@ -186,6 +186,8 @@ workflows:
   list:
     input:
       - group_names: []
+    output:
+      validations: <% task(find_validations).result %>
     tags:
       - tripleo-common-managed
     tasks:
@@ -193,6 +195,8 @@ workflows:
         action: tripleo.validations.list_validations groups=<% $.group_names %>
 
   list_groups:
+    output:
+      groups: <% task(find_groups).result %>
     tags:
       - tripleo-common-managed
     tasks: