Add python interpreter to ansible postconfig

In order to specify which version of python we should use for the
deployment, we need to pass in the python interpreter into the
postconfig where we are directly calling the ansible heat hook.

Change-Id: I9dfc72269f800395a9864c457a5a43f7590c8e75
Related-Blueprint: python3-support

extraconfig/post_deploy/standalone_post.yaml

@@ -36,6 +36,10 @@ parameters:
     type: string
     default: 'standalone'
     description: Cloud name for the clouds.yaml
+  PythonInterpreter:
+    type: string
+    description: The python interpreter to use for python and ansible actions
+    default: /usr/bin/python
 
 conditions:
 
@@ -55,6 +59,10 @@ resources:
     type: OS::Heat::SoftwareConfig
     properties:
       group: ansible
+      inputs:
+        - name: ansible_python_interpreter
+          description: Python interpreter to use for the ansible execution
+          default: {get_param: PythonInterpreter}
       config: |
         ---
         - name: StandalonePostConfig