Move qemu_audit.h helpers into shared code

Move qemu_audit.h helpers into shared code

The LXC and UML drivers can both make use of auditing. Move
the qemu_audit.{c,h} files to src/conf/domain_audit.{c,h}

* src/conf/domain_audit.c: Rename from src/qemu/qemu_audit.c
* src/conf/domain_audit.h: Rename from src/qemu/qemu_audit.h
* src/Makefile.am: Remove qemu_audit.{c,h}, add domain_audit.{c,h}
* src/qemu/qemu_audit.h, src/qemu/qemu_cgroup.c,
  src/qemu/qemu_command.c, src/qemu/qemu_driver.c,
  src/qemu/qemu_hotplug.c, src/qemu/qemu_migration.c,
  src/qemu/qemu_process.c: Update for changed audit API names