Fix CRI socket in Kubernetes >= 1.12.0 kubeadmin config (#3452)

Use CRI socket from parameter for V1Alpha3 configs instead of hardcoded
dockershim path

Author: ceache

pkg/minikube/bootstrapper/kubeadm/templates.go

@@ -60,7 +60,7 @@ bootstrapTokens:
   - authentication
 kind: InitConfiguration
 nodeRegistration:
-  criSocket: /var/run/dockershim.sock
+  criSocket: {{if .CRISocket}}{{.CRISocket}}{{else}}/var/run/dockershim.sock{{end}}
   name: {{.NodeName}}
   taints: []
 ---