qemu: live migration with non-shared storage for kvm

qemu: live migration with non-shared storage for kvm

Support for live migration between hosts that do not share storage was
added to qemu-kvm release 0.12.1.
It supports two flags:
-b migration without shared storage with full disk copy
-i migration without shared storage with incremental copy (same base image
shared between source and destination).

I tested the live migration without shared storage (both flags) for native
and p2p with and without tunnelling.  I also verified that the fix doesn't
affect normal migration with shared storage.