Add pull.yml file for tempest

TrivialFix

Change-Id: I5ba19671a36eb2aab3bda96dd66486422cbc9cf7

ansible/roles/tempest/tasks/pull.yml

+---
+- name: Pulling tempest image
+  kolla_docker:
+    action: "pull_image"
+    common_options: "{{ docker_common_options }}"
+    image: "{{ tempest_image_full }}"