ftests-066: avoid enabling controller on leaf cgroup node

ftests-066: avoid enabling controller on leaf cgroup node

cgroup v2, has no internal process constraint, where the process runs
only on the leaf node of the cgroup hierarchy and no controllers should
be enabled on the leaf cgroup node too. Let's not enable cpu controller
on the leaf cgroup node. Also, fix the expected stderr, accordingly
while migrating the tasks using cgclassify.

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>