* 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.