Allow venv python interpreter to be overridden

Change-Id: I1c062a56edf895287e6dec9a093ed924a146464c

defaults/main.yml

@@ -16,6 +16,9 @@
 ## Verbosity Options
 debug: False
 
+#python venv executable
+cloudkitty_venv_python_executable: "{{ openstack_venv_python_executable | default('python2') }}"
+
 # Set the host which will execute the shade modules
 # for the service setup. The host must already have
 # clouds.yaml properly configured.

tasks/main.yml

@@ -79,6 +79,7 @@
   import_role:
     name: "python_venv_build"
   vars:
+    venv_python_executable: "{{ cloudkitty_venv_python_executable }}"
     venv_build_constraints: "{{ cloudkitty_git_constraints }}"
     venv_build_distro_package_list: "{{ cloudkitty_devel_distro_packages }}"
     venv_install_destination_path: "{{ cloudkitty_bin | dirname }}"