support cgroup v1 mounted with noprefix #7087

Job	Run time
test (ubuntu-20.04, 1.22.x, rootless, -race)	7m 18s
cross-i386	1m 11s
test (ubuntu-20.04, 1.22.x, rootless)	6m 46s
test (ubuntu-20.04, 1.22.x, -race)	7m 48s
test (ubuntu-20.04, 1.22.x)	7m 7s
test (ubuntu-20.04, 1.23.x, rootless, -race)	7m 16s
test (ubuntu-20.04, 1.23.x, rootless)	7m 4s
test (ubuntu-20.04, 1.23.x, -race)	7m 54s
test (ubuntu-20.04, 1.23.x)	7m 6s
test (ubuntu-20.04, 1.23.x, criu-dev)	7m 41s
test (ubuntu-24.04, 1.22.x, rootless, -race)	9m 46s
test (ubuntu-24.04, 1.22.x, rootless)	9m 17s
test (ubuntu-24.04, 1.22.x, -race)	7m 49s
test (ubuntu-24.04, 1.22.x)	6m 47s
test (ubuntu-24.04, 1.23.x, rootless, -race)	9m 52s
test (ubuntu-24.04, 1.23.x, rootless)	9m 36s
test (ubuntu-24.04, 1.23.x, -race)	8m 0s
test (ubuntu-24.04, 1.23.x)	7m 28s
test (ubuntu-24.04, 1.23.x, criu-dev)	7m 57s
test (actuated-arm64-6cpu-8gb, 1.23.x, rootless)	11m 45s
test (actuated-arm64-6cpu-8gb, 1.23.x)	7m 58s
all-done	1s
	2h 43m 27s

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