Simplify the names of the minikube machine drivers

[afbjorklund]

With the docker-machine drivers gone, there is no need for "kvm2" and "qemu2" any more.

And there is no need for "generic" or "none" either, the drivers can be renamed in minikube.

• kvm
• ssh (renamed from "generic")
• native (renamed from "none")
• qemu

	// AliasKVM is driver name alias for kvm2
	AliasKVM = "kvm"
	// AliasSSH is driver name alias for ssh
	AliasSSH = "generic"
	// AliasNative is driver name alias for None driver
	AliasNative = "native"
	// AliasQEMU is the driver name alias for qemu2
	AliasQEMU = "qemu"

• rename "none" driver to "native" #7772
• Fork the machine driver "generic" to minikube, prepare for renaming it #9583

Previously, kvm1 and qemu1 were the drivers used for docker-machine.

We tried to rename "kvm" to libvirt for sanity, but that name failed to stick.

• https://github.com/machine-drivers/docker-machine-driver-qemu

• https://github.com/machine-drivers/docker-machine-driver-libvirt

[nirs]

kvm is the wrong name - both qemu and libvirt use kvm. The right name for the libvirt driver is libvirt. We can keep kvm and kvm2 as aliases do we don't break users.

[afbjorklund]

It originally came from here: https://github.com/dhiltgen/docker-machine-kvm (predating the qemu driver, but anyway)

[nirs]

If we want to be really correct, the name should be libvirt/kvm since libvirt supports also other drivers, but I think we have enough drivers ;-)