The old version of the script downloaded all binaries and generated file checksums locally.
This was a slow process since all binaries of all architectures needed to be downloaded.
The new version simply downloads the .sha256 files containing the binary checksum in text
form which saves a lot of traffic and time.
* 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
The main functions are wrapped by a sys.exit function which expects and
argument. The curent implementation isn't returning values in all cases.
This change ensures main functions return a value in all cases.