missing _cache_image() in libvirt driver

[Yun Mao]

pre_block_migration() might call self._cache_image, which is refactored away from the driver since change I0d01cb7d2fd67de2565b8d45d34f7846ad4112c2

[Michael Still (mikal)]

This wasn't picked up (among other reasons) because the test coverage for this method is poor -- none of the else block after "if not info['backing_file'] has tests, not the kernel and ram disk fetch.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/11395

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/11395
Committed: http://github.com/openstack/nova/commit/5738e6a470eaec9389a15689cf5be8ac9e2115ac
Submitter: Jenkins
Branch: master

commit 5738e6a470eaec9389a15689cf5be8ac9e2115ac
Author: Michael Still <email address hidden>
Date: Wed Aug 15 17:57:14 2012 +1000

    Port pre_block_migration to new image caching

    This resolves bug 1036419, which was a missed call to _cache_image
    when that method was refactored away.

    Change-Id: I68f6aced5382e378dc707fd003d27dbfdd24aded