archive2disk README and implementation differ on argument for disk device

[Jason DeTiberus]

Expected Behaviour

Readme and implementation of archive2disk to match

Current Behaviour

The readme references DEST_DISK, but the code looks for BLOCK_DEVICE

Possible Solution

Either update the documentation or update the implementation to match. DEST_DISK seems to align better with other actions, but would technically be a breaking change from the current implementation.

Context

I noticed it when trying to create a new action and using the existing actions as reference

Your Environment

• Operating System and version (e.g. Linux, Windows, MacOS): Linux

• How are you running Tinkerbell? Using Vagrant & Libvirt