Return a value for storage_type when reading qemu disks (or remove the need for it entirely)

[doransmestad]

I'm working on a pull request for the terraform provider, and it looks like the qemuDisk's attribute storage_type is required for the creation/update of disks within a qemu resource, but that value is not returned by a call to NewConfigQemuFromApi. This is unfortunate as I'm not able to be sure of the current value to use for storage_type after creation (to detect drift and correctly update the terraform state).

Ideally, we could remove the need for storage_type as it appears to only be used here: https://github.com/Telmate/proxmox-api-go/blob/master/proxmox/config_qemu.go#L900 in order to format the disk path correctly. Perhaps we could issue another API query to proxmox to list storage types (/storage/<storage_name>) and pull out the type attribute from there? Then we wouldn't need storage_type at all.

Or, if not the above, when a VM is read perhaps we can re-use the logic from line 900 above to return the storage_type format required (dir vs rbd for example).

Thoughts? I'm happy to attempt a contribution of either approach depending on preference.

[yukron]

PR #94 would resolve this, also adding "format" key to Reads.