* Move all but mock provider out of tree
These have all been moved to repos under github.com/virtual-kubelet.
* Introduce a providers.Store
This essentially moves the the old register/ handling into a first class
object that can be controlled from the CLI rather than through build
tags deep in the code.
This actually would have made it a bit easier to build the provider
repos and makes the cmd/ code more re-usable.
This starts the work of having a `NodeProvider` which is responsible for
providing node details.
It splits the responsibilities of node management off to a new
controller.
The primary change here is to add the framework pieces for node
management and move the VK CLI to use this new controller.
It also adds support for node leases where available. This can be
enabled via the command line (disabled by default), but may fall back if
we find that leaess aren't supported on the cluster.
