cgclear: delete cgroups from config file

cgclear: delete cgroups from config file

cgclear should be able to 'uload' cgroups (and mounts) as specified in
given config file - as exact opposite of cgconfigparser.

This patch adds new options '-c <config_file>' and '-C <directory with config
files> just for this purpose. These options can be specified multiple times.

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