Keeping user volumes persistent

When using RancherOS, only specific directories keep the data defined by the user-volumes parameter persistent.

To add additional persistent user-volumes, for example, add the /var/openebs directory:

$ ros config set rancher.services.user-volumes.volumes \[/home:/home,/opt:/opt,/var/lib/kubelet:/var/lib/kubelet,/etc/kubernetes:/etc/kubernetes,/var/openebs]
$ system-docker rm all-volumes
$ reboot

After rebooting, data in the specified directories will be persistent.