Move QEMU monitor socket in /var/lib/libvirt/qemu

Move QEMU monitor socket in /var/lib/libvirt/qemu

Separate the guest created QEMU monitor socket location
from the libvirtd create XML / PID data files, to improve
security separation when running QEMU non-root

* libvirt.spec.in: Leave /var/run/libvirt/qemu as root:root
* src/qemu_conf.h: Add libDir and cacheDir directory paths
* src/qemu_driver.c: Move QEMU monitor socket from
  stateDir to libDir to avoid making security critical directory
  accessible to QEMU guests.
* src/util.c: Delay running hook till after damonizing to
  ensure pidfile is still written before changing UID/GID