Remove minikube support for docker machine provisioners #22384
Description
There is no need to carry all the different provisioners, since they are unused anyway.
Their main purpose was to install docker on the machine, which is no longer needed...
vendor/github.com/docker/machine/
├── libmachine
│ ├── provision
│ │ ├── arch.go
│ │ ├── boot2docker.go
│ │ ├── centos.go
│ │ ├── configure_swarm.go
│ │ ├── coreos.go
│ │ ├── debian.go
│ │ ├── fedora.go
│ │ ├── oraclelinux.go
│ │ ├── rancheros.go
│ │ ├── redhat.go
│ │ ├── redhat_ssh_commander.go
│ │ ├── suse.go
│ │ ├── ubuntu_systemd.go
│ │ ├── ubuntu_upstart.go
They (libmachine/provision) are replaced with internal versions in pkg/provision instead.
Currently they don't do any provisioning, but just generate certificates and some config.
For the "native" and "ssh" drivers, the user is reponsible for installing the container runtime.
Eventually it will be replaced with a new mechanism, that will install more than just docker:
It needs to know which Kubernetes version to prepare for, and install CRI-tools and CNI-plugins.