support cgroup v1 mounted with noprefix #7090

Job	Run time
cross-i386	1m 17s
test (ubuntu-20.04, 1.22.x, rootless, -race)	7m 9s
test (ubuntu-20.04, 1.22.x, rootless)	6m 55s
test (ubuntu-20.04, 1.22.x, -race)	7m 47s
test (ubuntu-20.04, 1.22.x)	7m 2s
test (ubuntu-20.04, 1.23.x, rootless, -race)	7m 16s
test (ubuntu-20.04, 1.23.x, rootless)	6m 52s
test (ubuntu-20.04, 1.23.x, -race)	7m 50s
test (ubuntu-20.04, 1.23.x)	7m 18s
test (ubuntu-20.04, 1.23.x, criu-dev)	7m 58s
test (ubuntu-24.04, 1.22.x, rootless, -race)	9m 44s
test (ubuntu-24.04, 1.22.x, rootless)	9m 29s
test (ubuntu-24.04, 1.22.x, -race)	8m 0s
test (ubuntu-24.04, 1.22.x)	6m 56s
test (ubuntu-24.04, 1.23.x, rootless, -race)	10m 5s
test (ubuntu-24.04, 1.23.x, rootless)	9m 33s
test (ubuntu-24.04, 1.23.x, -race)	8m 18s
test (ubuntu-24.04, 1.23.x)	7m 39s
test (ubuntu-24.04, 1.23.x, criu-dev)	8m 4s
test (actuated-arm64-6cpu-8gb, 1.23.x, rootless)	11m 46s
test (actuated-arm64-6cpu-8gb, 1.23.x)	8m 1s
all-done	1s
	2h 45m 0s

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