OpenStack docs: add blockstorage volumes info
OpenStack docs: add blockstorage volumes info

Add notes, available parameters and basic example of how to use
OpenStack Block Storage volume as a root volume of an instance.

mitchellh/packer,timsutton/packer,rnaveiras/packer,timsutton/packer,tb3088/packer,tas50/packer,dave2/packer,dave2/packer,mkuzmin/packer,grubernaut/packer,mkuzmin/packer,mitchellh/packer,paulmey/packer,youhong316/packer,timsutton/packer,ricardclau/packer,paulmey/packer,tas50/packer,dave2/packer,tas50/packer,grubernaut/packer,timsutton/packer,grubernaut/packer,bryson/packer,tb3088/packer,dave2/packer,tas50/packer,tb3088/packer,hashicorp/packer,ricardclau/packer,ricardclau/packer,tas50/packer,youhong316/packer,rnaveiras/packer,paulmey/packer,hashicorp/packer,bryson/packer,tas50/packer,youhong316/packer,bryson/packer,rnaveiras/packer,mitchellh/packer,timsutton/packer,pecigonzalo/packer,dave2/packer,bryson/packer,timsutton/packer,tb3088/packer,rnaveiras/packer,rnaveiras/packer,paulmey/packer,youhong316/packer,grubernaut/packer,tb3088/packer,ricardclau/packer,mitchellh/packer,paulmey/packer,pecigonzalo/packer,ricardclau/packer,hashicorp/packer,mkuzmin/packer,hashicorp/packer,bryson/packer,paulmey/packer,ricardclau/packer,rnaveiras/packer,mkuzmin/packer,mkuzmin/packer,mitchellh/packer,youhong316/packer,bryson/packer,pecigonzalo/packer,youhong316/packer,grubernaut/packer,dave2/packer,mkuzmin/packer,grubernaut/packer,tb3088/packer,pecigonzalo/packer