Add retries to requirement package install

The requirement package install task includes two actions:
1. update the apt cache
2. install the packages from a remote mirror

Both of these may fail due to transient issues and should
therefore be retried.

Change-Id: I992c045273646995a6d9cebb6ea10db214ff588a

tasks/openstack_hosts_configure_apt.yml

@@ -40,6 +40,10 @@
     state: "{{ openstack_hosts_package_state }}"
     update_cache: yes
     cache_valid_time: "{{ cache_timeout }}"
+  register: _install_packages
+  until: _install_packages | success
+  retries: 5
+  delay: 2
 
 - name: Remove any old UCA repository using the old filename
   file: