Enable delegating all downloads (binaries, images, kubeadm images) (#4420)

* Download to delegate and sync files when download_run_once

* Fail on error after saving container image

* Do not set changed status when downloaded container was up to date

* Only sync containers when they are actually required

Previously, non-required images (pull_required=false as
image existed on target host) were synced to the target
hosts. This failed as the image was not downloaded to
the download_delegate and hence was not available for
syncing.

* Sync containers when only missing on some hosts

* Consider images with multiple repo tags

* Enable kubeadm images pull/syncing with download_delegate

* Use kubeadm images list to pull/sync

'kubeadm config images pull' is replaced by collecting the images
list with 'kubeadm config images list' and using the commonly
used method of pull/syncing the images.

* Ensure containers are downloaded and synced for all hosts

* Fix download/syncing when download_delegate is a kubernetes host

roles/download/tasks/download_file.yml

@@ -15,7 +15,33 @@
     - download.file
     - group_names | intersect(download.groups) | length
 
-- name: file_download | Download item
+# As in 'download_container.yml':
+#   In Ansible 2.4 omitting download delegate is broken. Move back
+#   to one task in the future.
+- name: file_download | Download item (delegate)
+  get_url:
+    url: "{{download.url}}"
+    dest: "{{download.dest}}"
+    sha256sum: "{{download.sha256 | default(omit)}}"
+    owner: "{{ download.owner|default(omit) }}"
+    mode: "{{ download.mode|default(omit) }}"
+    validate_certs: "{{ download_validate_certs }}"
+    url_username: "{{ download.username|default(omit) }}"
+    url_password: "{{ download.password|default(omit) }}"
+    force_basic_auth: "{{ download.force_basic_auth|default(omit) }}"
+  register: get_url_result
+  until: "'OK' in get_url_result.msg or 'file already exists' in get_url_result.msg"
+  retries: 4
+  delay: "{{ retry_stagger | default(5) }}"
+  delegate_to: "{{ download_delegate }}"
+  when:
+    - download_run_once
+    - download.enabled
+    - download.file
+    - group_names | intersect(download.groups) | length
+  run_once: yes
+
+- name: file_download | Download item (all)
   get_url:
     url: "{{download.url}}"
     dest: "{{download.dest}}"
@@ -31,6 +57,7 @@
   retries: 4
   delay: "{{ retry_stagger | default(5) }}"
   when:
+    - not download_run_once
     - download.enabled
     - download.file
     - group_names | intersect(download.groups) | length