Retry apt cache update

This task is causing some test failures from time
to time. Implementing a retry should help to reduce
transient failures.

Change-Id: I2a71b9f5d8af4ada504072f9236f49be52eafee8

common-tasks/test-force-package-cache-update.yml

@@ -16,5 +16,9 @@
 - name: First ensure apt cache is always refreshed
   apt:
     update_cache: true
+  register: _update
+  retries: 5
+  delay: 2
+  until: _update | succeeded
   when:
     - ansible_pkg_mgr == 'apt'