Problem:

A false-negative in check-config.sh for cgroups v2 systems was fixed but the
commit introduced a regression based on a small assumption that content of
/sys/fs/cgroup/cgroup.controllers would have the same format as the content
of /proc/self/cgroup. It doesn't.

Solution:

This just tweaks the regex to count occurrences of either cgroup
subsystem-names on each line (as occurs in the sysfs pseudo-file), or those
names with colons either side (as occurs in the procfs pseudo-file).
Signed-off-by: Rowan Thorpe <rowan@rowanthorpe.com>