add unit test for GetDNSIP
add unit test for GetDNSIP

Signed-off-by: Zhou Hao <f577ade201aa03d612c19915a089dc6084d45cd9@cn.fujitsu.com>

warmchang/minikube,kubernetes/minikube,warmchang/minikube,warmchang/minikube,dlorenc/minikube,dlorenc/minikube,warmchang/minikube,kubernetes/minikube,kubernetes/minikube,dalehamel/minikube,warmchang/minikube,kubernetes/minikube,warmchang/minikube,kubernetes/minikube,dlorenc/minikube,dlorenc/minikube,dalehamel/minikube,kubernetes/minikube,kubernetes/minikube,dalehamel/minikube,dlorenc/minikube,warmchang/minikube,dlorenc/minikube,dlorenc/minikube,dlorenc/minikube