vagrant: add ability to use drives in the VMs

When testing deployments of SDS, it is quite useful to get a Kubernetes
env with nodes having dedicated drives.
You can now enable this by setting: kube_node_instances_with_disks: true

Also you can chose the amount of drives per machine and their respective
size:

* kube_node_instances_with_disks_number: 10
* kube_node_instances_with_disks_size: "20G"

Signed-off-by: Sébastien Han <seb@redhat.com>