Move QEMU command line management into a separate file

Move QEMU command line management into a separate file

The qemu_conf.c code is doing three jobs, driver config file
loading, QEMU capabilities management and QEMU command line
management. Move the command line code into its own file

* src/qemu/qemu_command.c, src/qemu/qemu_command.h: New
  command line management code
* src/qemu/qemu_conf.c, src/qemu/qemu_conf.h: Delete command
  line code
* src/qemu/qemu_conf.h, src/qemu_conf.c: Adapt for API renames
* src/Makefile.am: add src/qemu/qemu_command.c
* src/qemu/qemu_monitor_json.c, src/qemu/qemu_monitor_text.c: Add
  import of qemu_command.h