Avoid possible live-lock in vcpu_migrate

Avoid possible live-lock in vcpu_migrate

If vcpu_migrate is called for two vcpus active on different cpus
resulting in swapping the cpus, a live-lock could occur as both
instances try to take the scheduling lock of the physical cpus in
opposite order.

To avoid this problem the locks are always taken in the same order
(sorted by the address of the lock).

Signed-off-by: Jueregn Gross <juergen.gross@ts.fujitsu.com>