libvirt: disk_bus setting is being lost when migration is reverted

finish_revert_migration() should use image_meta, if it exist,
when constructing the disk_info.

Closes-Bug: #1389850
Change-Id: Ia373771eaaad4154a2aa0695bf3878713a68dd9f
Merge "libvirt: disk_bus setting is being lost when migration is reverted"