* qemud/libvirtd_qemu.aug, qemud/test_libvirtd_qemu.aug,
   src/qemu.conf: Add 'cgroups_controllers' and 'cgroups_device_acl'
   parameters
 * src/qemu_conf.h, src/qemu_conf.c: Load & parse configuration params
   for cgroups
 * src/qemu_driver.c: Only use cgroups controllers that are activated,
   and use configured device whitelist instead of default, if set.