prevent resize when multiple ephemeral disks

Change-Id: Ifa586b206e110500c95f30e944934efe56c63df5
tidy up migrate_disk_and_power_off

Change-Id: Id8973eff469c012f64df9d1b67befb3d11b6688b
hack up copying across multiple ephemeral disks

Change-Id: I99b77d68959562536c658784ca31ead01b15b1a9
pick up multiple ephemeral disks on the destination

Change-Id: I8dd11a64a6939e9934dcd1875f94da953e2ea67f