Libcgroup: added cgconfig.service unit for systemd.

Libcgroup: added cgconfig.service unit for systemd.

The cgconfig.service unit file should create all groups in
/etc/cgconfig.conf and (if not overriden in the config file) with sticky
bit on their tasks file. On service stop, only control groups specified in the
config file are cleared and only if they are empty (i.e. no subgroups and no
processes inside).

Please review carefully, especially the ordering. I want the service to
start as early as possible, but not before local filesystem is ready.

Changelog:
 - updated After/Before dependencies

Signed-off-by: Jan Safranek <jsafrane@redhat.com>