Switch over to passing a callback table to QEMU monitor

Switch over to passing a callback table to QEMU monitor

With addition of events there will be alot of callbacks.
To avoid having to add many APIs to register callbacks,
provide them all at once in a big table

* src/qemu/qemu_driver.c: Pass in a callback table to QEMU
  monitor code
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h Replace
  the EOF and disk secret callbacks with a callback table