Handle refactoring of libvirt image caching.
Handle refactoring of libvirt image caching.

This patch handles the refactored image caching for libvirt. The
new scheme keeps multiple copies of an image:

  <fingerprint>:        the image from glance
  <fingerprint>_<size>: the resized image

The resized image is then copied or CoW'd across to the instance
disk. We also want to keep original images from glance longer than
we keep the resized images, as they're smaller and this reduces the
load on glance. Therefore a new flag to handle the differing rules
has been added.

Change-Id: If6d9471b3d67cb8fac3f168b1b4a3cd57b9cc9a7

n0ano/ganttclient