CORD-1868 Add always_pull_xos_images flag

Change-Id: Ie7cdaa5d4785392d8bfeae36ca08170282011bb4
(cherry picked from commit 874d56d774f02023fd82c79c53aa06e928443e9c)
diff --git a/roles/xos-up/tasks/main.yml b/roles/xos-up/tasks/main.yml
index 38d3b47..09ae4a2 100644
--- a/roles/xos-up/tasks/main.yml
+++ b/roles/xos-up/tasks/main.yml
@@ -26,3 +26,4 @@
   docker_service:
     project_name: "{{ cord_profile | regex_replace('\\W','') }}"
     project_src: "{{ head_cord_profile_dir }}"
+    pull: "{{ always_pull_xos_images | default('false') }}"