* containerd: add hashes for 1.5.8 and 1.4.12 and make 1.5.8 the new default
* containerd: make nerdctl mandatory for container_manager = containerd
* nerdctl: bump to version 0.14.0
* containerd: use nerdctl for image manipulation
* OpenSuSE: install basic nerdctl dependencies
* download file
* download containers
* fix push image to nodes
* pull if none image on host
* fix
* improve docker image tag checks.
do not pull already cached images
* rebase fix merge conflict
* add support download_run_once when upgrade and scale cluster
add some test with download_run_once
* set default values to temp flag for every download cycle
* add save,load abilty for containerd and crio when download_run_once=true
* return redefine image save/load command to set_docker_image_facts.yml
* move set command to set_container_facts
* ctr in containerd_bin_dir
* fix order of ctr image export arguments
* temporary disable download_run_once for containerd and crio
due https://github.com/containerd/containerd/issues/4075
* remove unused files
* fix strict yaml linter warning and errors
* refactor logical conditions to pull and cache container images
* remove comment due lint check
* document role
* remove image_load_on_localhost, because cached images are always loaded to docker on remote sites
* remove XXX from debug output
* File and container image downloads are now cached localy, so that repeated vagrant up/down runs do not trigger downloading of those files. This is especially useful on laptops with kubernetes runnig locally on vm's. The total size of the cache, after an ansible run, is currently around 800MB, so bandwidth (=time) savings can be quite significant.
* When download_run_once is false, the default is still not to cache, but setting download_force_cache will still enable caching.
* The local cache location can be set with download_cache_dir and defaults to /tmp/kubernetes_cache
* A local docker instance is no longer required to cache docker images; Images are cached to file. A local docker instance is still required, though, if you wish to download images on localhost.
* Fixed a FIXME, wher the argument was that delegate_to doesn't play nice with omit. That is a correct observation and the fix is to use default(inventory_host) instead of default(omit). See ansible/ansible#26009
* Removed "Register docker images info" task from download_container and set_docker_image_facts because it was faulty and unused.
* Removed redundant when:download.{container,enabled,run_once} conditions from {sync,download}_container.yml
* All features of commit d6fd0d2aca by Timoses <timosesu@gmail.com>, merged May 1st 2019, are included in this patch. Not all code was included verbatim, but each feature of that commit was checked to be working in this patch. One notable change: The actual downloading of the kubeadm images was moved to {download,sync)_container, to enable caching.
Note 1: I considered splitting this patch, but most changes that are not directly related to caching, are a pleasant by-product of implementing the caching code, so splitting would be impractical.
Note 2: I have my doubts about the usefulness of the upload, download and upgrade tags in the download role. Must they remain or can they be removed? If anybody knows, then please speak up.
