added docker to supported drivers

pkg/minikube/driver/driver.go

@@ -26,6 +26,8 @@ import (
 )
 
 const (
+	// Kubernetes in container using docker driver
+	KicDocker = "docker"
 	// Mock driver
 	Mock = "mock"
 	// None driver

pkg/minikube/driver/driver_darwin.go

@@ -25,6 +25,7 @@ var supportedDrivers = []string{
 	VMwareFusion,
 	HyperKit,
 	VMware,
+	KicDocker,
 }
 
 func VBoxManagePath() string {

pkg/minikube/driver/driver_linux.go

@@ -28,6 +28,7 @@ var supportedDrivers = []string{
 	KVM2,
 	VMware,
 	None,
+	KicDocker,
 }
 
 // VBoxManagePath returns the path to the VBoxManage command

pkg/minikube/driver/driver_windows.go

@@ -32,6 +32,7 @@ var supportedDrivers = []string{
 	VMwareFusion,
 	HyperV,
 	VMware,
+	KicDocker,
 }
 
 func VBoxManagePath() string {