Make the --label-whitelist effective. Previously, it was unused and had no effect. Also, add simple unit test for that.
Remove functionality that was not interacting with Kubernetes API. Makes the architecture a bit simpler and simplifies testing.
Move most of the code under cmd/nfd-master and cmd/nfd-worker into new packages pkg/nfd-master and pk/nfd-worker, respectively. Makes extending unit tests to "main" functions easier.
