fix HVM log dirty issue

fix HVM log dirty issue

These patches fix some issues for HVM log dirty in qemu:
* Add necessary logging dirty in qemu to avoid guest error with
intensive disk access when live migration
* Take place of shared memory between qemu and migration tools by new
added hypercall, which is clean and simple

Signed-Off-By: Zhai, Edwin <edwin.zhai@intel.com>
Also revert commit 32710fbdc75e055f73a63d246737ce615b9109e9.
  "[stubdom] fix the crash of HVM live migration with intensive disk access"
 as this is the proper fix.   -iwj