Fix cache update after initial apt_repository fail

If apt_repository fails to update the apt cache after updating the
configuration, retries don't register there was a change and so no
attempt is made to update the cache by the module on the second attempt.
This failure can result in a failure to install packages.

This change adds an apt module task to update the cache if the
apt_repository task registers a change. This means updating the cache
will get retried on failure and no longer fail silently.

Change-Id: Id059dbec3466cb1ef3ea567249f52384a8ade515
Partial-Bug: #1750656

tasks/install_apt.yml

@@ -46,29 +46,37 @@
       tags:
         - rabbitmq-apt-keys
 
+# When updating the cache in the apt_repository
+# task, and the update fails, a retry does not
+# detect a change the second attempt and therefore
+# does not update the cache, resulting in a changed
+# repo config, but no updated cache. To work around
+# this bug we implement the change of repo config
+# and the cache update as two seperate tasks.
 - name: Add rabbitmq repo
   apt_repository:
     repo: "{{ rabbitmq_repo.repo }}"
     state: "{{ rabbitmq_repo.state }}"
     filename: "{{ rabbitmq_repo.filename | default(omit) }}"
-  register: add_repos
-  until: add_repos|success
-  retries: 5
-  delay: 2
+  register: add_rabbitmq_repos
   when:
     - rabbitmq_install_method == 'external_repo'
   tags:
     - rabbitmq-repos
 
+# When updating the cache in the apt_repository
+# task, and the update fails, a retry does not
+# detect a change the second attempt and therefore
+# does not update the cache, resulting in a changed
+# repo config, but no updated cache. To work around
+# this bug we implement the change of repo config
+# and the cache update as two seperate tasks.
 - name: Add erlang repo
   apt_repository:
     repo: "{{ rabbitmq_erlang_repo.repo }}"
     state: "{{ rabbitmq_erlang_repo.state }}"
     filename: "{{ rabbitmq_erlang_repo.filename | default(omit) }}"
-  register: add_repos
-  until: add_repos|success
-  retries: 5
-  delay: 2
+  register: add_erlang_repos
   tags:
     - rabbitmq-repos
 
@@ -77,9 +85,9 @@
     pkg: "{{ rabbitmq_dependencies | deprecated(rabbitmq_apt_packages, 'rabbitmq_apt_packages', 'rabbitmq_dependencies', 'Ocata') }}"
     state: "{{ rabbitmq_package_state }}"
     update_cache: yes
-    cache_valid_time: "{{ cache_timeout }}"
+    cache_valid_time: "{{ (add_rabbitmq_repos | changed or add_erlang_repos | changed) | ternary('0', cache_timeout) }}"
   register: install_packages
-  until: install_packages|success
+  until: install_packages | success
   retries: 5
   delay: 2
   tags: