utils_cgroup: Add option to check if cgconfig service exists

On systemd enabled machines the cgroup subsystem is managed by systemd
itself. The logic in utils_cgroup.cgconfig_is_running() returns False even
if cgroups are running in systemd.

This patch adds function cgconfig_exists() that returns True if cgconfig is
available to enable skipping tests.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
utils_cgroup: Strip the slash from cgroup path

We have to strip the slash from cgroup path because the "join" function
takes the last element starting with slash as the root path.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
utils_cgroup: Fix regexp for cgroup controllers

On some systems the cpu and cpuacct controllers are mounted together
like cpu,cpuacct and we should count with it.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>