Support format-agnostic copy-on-write provisioning of VM instances through IBM GPFS file system

Instance file creation through copy-on-write mechanism is fast, but it is supported for qcow2 images only. This blueprint proposes the use of file system level copy-on-write function provided by GPFS to quickly create instance files regardless of the image format. In addition, downloading of the master image into hypervisor node from the image repository can also be avoided if the master images in image store backend and the instance files on the hypervisor nodes share the same cluster file system.