On internet I found this: RancherVM Images.
I have created the qcow2 image containing my edited Linux VM how to add to docker and see it from RancherVM web menu?
I understand how to do. First create or convert a qcow2 compressed image(is the qemu format) Then create a dockerfile like this and rename it Dockerfile
FROM rancher/vm-base:0.0.1 COPY centos.img /base_image/centos7.img CMD ["-m 2002m"]
then import in docker,of course do this where you copied the image(in my case is /root/centos.img and pwd is root)
docker build -t "centos7:kvm"
Then open ranchervm webgui,do "create instance" and put centos7:kvm in "image",setup other things how you like it and click ok You can run the docker image created via kvm via vnc on browser.