Pull out all the QEMU monitor interaction code to a separate
file. This will make life easier when we need to drop in a
new implementation for the forthcoming QMP machine friendly
monitor support.

Next step is to add formal APIs for each monitor command,
and remove direct commands for sending/receiving generic
data.

* src/Makefile.am: Add qemu_monitor.c to build
* src/qemu/qemu_driver.c: Remove code for monitor interaction
* src/qemu/qemu_monitor_text.c, src/qemu/qemu_monitor_text.h: New
  file for monitor interaction
* po/POTFILES.in: Add src/qemu/qemu_monitor_text.c