Use block_device_info at post_live_migration_at_destination

post_live_migration_at_destination make libvirt.xml to destination
host. when execute (live) block migration for vm made by bootable
volume, method post_live_migration_at_destination write a
libvirt.xml in destination host.
but it missed block disk information so moved libvirt.xml always
has a wrong disk information.
I add block_device_info in blockinfo.get_disk_info at
post_live_migration_at_destination.
This change will make libvirt.xml with valid block disk information.

Closes-Bug: 1271780
(cherry picked from commit 0486647e1c85947bc48cbdd279b3f49824a6e692)

Conflicts:
	nova/tests/virt/libvirt/test_libvirt.py
	nova/virt/libvirt/driver.py

Change-Id: I31b3f2ef5f03f9ef61524bdb7ae089b18e4cd254
Merge "Use block_device_info at post_live_migration_at_destination" into stable/havana