Enable overriding the service setup host python interpreter

In order to enable the service setup host python interpreter to
be changed easily, we make it a variable. This will be useful
when someone sets the service setup host to be the utility
container, because we'll be able to set this var by default.

Change-Id: Ia3b8ac0cc8ca895c39b20eac30763ad4873f78b1

defaults/main.yml

@@ -26,6 +26,7 @@ tacker_ceilometer_enabled: False
 # for the service setup. The host must already have
 # clouds.yaml properly configured.
 tacker_service_setup_host: "{{ openstack_service_setup_host | default('localhost') }}"
+tacker_service_setup_host_python_interpreter: "{{ openstack_service_setup_host_python_interpreter | default((tacker_service_setup_host == 'localhost') | ternary(ansible_playbook_python, ansible_python['executable'])) }}"
 
 # Set the package install state for distribution packages
 # Options are 'present' and 'latest'

tasks/tacker_service_setup.yml

@@ -23,8 +23,7 @@
 - name: Setup the service
   delegate_to: "{{ tacker_service_setup_host }}"
   vars:
-    ansible_python_interpreter: >-
-      {{ (tacker_service_setup_host == 'localhost') | ternary(ansible_playbook_python, ansible_python['executable']) }}
+    ansible_python_interpreter: "{{ tacker_service_setup_host_python_interpreter }}"
   block:
     - name: Add service to the keystone service catalog
       os_keystone_service: