Use correct variable for sso_callback_template deployment

The sso_callback_template file needs to be deployed for a
Keystone SP, not IDP. This patch fixes the conditional.

Closes-Bug: #1772772
Change-Id: I420e291807434382b4d3cd4c8809c7540a419f5a

releasenotes/notes/sso-callback-template-cf720ab7f6fc2461.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The conditional that determines whether the ``sso_callback_template.html``
+    file is deployed for federated deployments has been fixed.

tasks/keystone_post_install.yml

@@ -96,7 +96,7 @@
     group: "{{ keystone_system_group_name }}"
     mode: "0644"
   when:
-    - keystone_idp != {}
+    - keystone_sp != {}
   notify:
     - Manage LB
     - Restart uWSGI
@@ -107,7 +107,7 @@
     path: "/etc/keystone/sso_callback_template.html"
     state: absent
   when:
-    - keystone_idp == {}
+    - keystone_sp == {}
   notify:
     - Manage LB
     - Restart uWSGI