Add retries to apt update in cache proxy task

When apt update was added to the package-cache-proxy.yml task,
the retries and delay fields were omitted.

Change-Id: I8e86b524269e3bf4ba2b5889d51ebf64d86472c8

playbooks/common-tasks/package-cache-proxy.yml

@@ -33,6 +33,8 @@
 - name: Update apt when proxy is added
   apt:
     update_cache: yes
+  retries: 5
+  delay: 2
   when:
     - apt_proxy_dropped | changed