XenAPINFS: Copy image from glance

XenAPINFS: Copy image from glance

related to blueprint xenapinfs-glance-integration

This change is using the glance xenapi plugin to copy a glance image to
a xenapinfs backed volume. It slightly differs from the reference
implementation, as this implementation is composed of three steps:
- create volume
- overwrite the created volume with the one downloaded from glance
- resize the volume
As opposed to fill the bytes from glance to the created image. This
approach works more effective with XenServer type semi ovf tgz -ed vhds.

Change-Id: I2345f6bb355aa285eee0455380c580e4724f004e