DevStack: Add configuration for boot-from-volume
DevStack: Add configuration for boot-from-volume

This patch enables boot-from-volume feature for DevStack with VMs.
- Add parameters for setting storage interface.
- Set node property for iscsi boot.
- Create volume connectors.

Change-Id: I1085bb8d44e3dbae61243dd9b65d17db33c505be
Partial-Bug: #1559691

pshchelo/ironic,pshchelo/ironic,openstack/ironic,openstack/ironic