Introduce TCP live migration protocol

Introduce TCP live migration protocol

This patch introduces a tcp protocol for live migration.  It can be used as
follows:

qemu-system-x86_64 -hda ~/images/linux-test.img -monitor stdio
 <vm runs for a while>
(qemu) migrate tcp:localhost:1025

On the same system:

qemu-system-x86_64 -hda ~/images/linux-test.img -incoming
tcp:localhost:1025

The monitor can be interacted with while waiting for an incoming live
migration.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5478 c046a42c-6fe2-441c-8c8c-71466251a162