Rename api-paste and policy configuration files

The api-paste file was incorrectly named api_paste.ini when implemented
on the designate server, and therefore wasn't being used.

The policy.json template file was renamed to policy.json.j2 to keep
consistent with conventions in OpenStack-Ansible. This eases the process
for updating the files automatically through convenience scripts.

tasks/designate_post_install.yml

@@ -27,11 +27,11 @@
       dest: "/etc/designate/designate.conf"
       config_overrides: "{{ designate_designate_conf_overrides }}"
       config_type: "ini"
-    - src: "api_paste.ini.j2"
+    - src: "api-paste.ini.j2"
       dest: "/etc/designate/api_paste.ini"
       config_overrides: "{{ designate_api_paste_ini_overrides }}"
       config_type: "ini"
-    - src: "policy.json"
+    - src: "policy.json.j2"
       dest: "/etc/designate/policy.json"
       config_overrides: "{{ designate_policy_overrides }}"
       config_type: "json"