When attaching to an external QEMU process, it is neccessary
to check if the process is using KVM or not. This can be done
using a monitor command

* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
  src/qemu/qemu_monitor_json.c, src/qemu/qemu_monitor_json.h,
  src/qemu/qemu_monitor_text.c, src/qemu/qemu_monitor_text.h: Add
  API for checking if KVM is enabled