Ansible syntax fix and added message decrypt.

* Decrypt message which is base64 encoded in secrets
* read change_url from zuul dictionary instead of its
  subelement items

Change-Id: I2137be52d4ad8c0a158b6192b6e0a08527c60328
Relates-To: #196

playbooks/airship-airshipctl-update-github-issues.yaml

@@ -21,7 +21,7 @@
       script: >
         zuul.d/scripts/update_github_issues.py "{{ github_credentials.username }}" \
           "{{ github_credentials.password }}" \
-          "{{ zuul.message }}" \
-          "{{ zuul.items[0].change_url }}"
+          "{{ zuul.message | b64decode }}" \
+          "{{ zuul.change_url }}"
       args:
         executable: python3