* Decouple role kubespray-defaults from download
Avoids doing re-importing the download role on every invocation of
kubespray-defaults (and skipping everything).
This has a measurable effect on playbook performance.
* Update docs refering to moved download defaults
This fixes the following failures:
./contrib/offline/README.md:14:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ ./manage-offline-container-i..."]
./contrib/offline/README.md:20:1 MD014/commands-show-output Dollar signs used before commands without showing output [Context: "$ ./manage-offline-container-i..."]