Implement LIO-based volume support by interfacing with targetd

The purpose of this blueprint is to provide a Cinder volume driver that provides volumes driven by the LIO unified target. This is intended to be a more modern option for users that would have used the tgtd driver in the past.

It will plug in to Cinder as an alternative iSCSI TargetAdmin class, and be driven by the iSCSI driver.

LIO: http://www.linux-iscsi.org/

targetd: https://github.com/agrover/targetd

From the targetd README, "targetd turns Linux into a remotely-configurable storage appliance. It supports an HTTP/jsonrpc-2.0 interface to let a remote administrator allocate volumes from an LVM volume group, and export those volumes over iSCSI."

Note: This effort is using the libstoragemgmt Python library rather than targetd JSON-RPC.
http://libstoragemgmt.sourceforge.net/