dbuild detects if the kernel is using cgroupv2 by checking if the
cgroup2 filesystem is mounted on /sys/fs/cgroup. However, on Ubuntu
20.10, the cgroup filesystem is mounted on /sys/fs/cgroup and the
cgroup2 filesystem is mounted on /sys/fs/cgroup/unified. This second
mount matches the search expression and gives a false positive.
Fix by adding a space at the end; this will fail to match
/sys/fs/cgroup/unified.
Closes#8355
ec4d91f9eb