add relevant documentation/examples for working with multiple volumes for the various hypervisors/cloud deploys

[eyberg]

we can create sep tickets to track these but:

• [ ] local/kvm volumes
• [ ] gcloud volumes
• [ ] aws volumes
• [ ] esx volumes
• [ ] openstack volumes
• [ ] azure volumes

[eyberg]

not sure why this was put in examples and not docs:

https://github.com/nanovms/ops-examples/tree/master/golang/05-empty-volume https://github.com/nanovms/ops-examples/tree/master/golang/06-non-empty-volume