cgroup: use default sandbox cgroup path #924

Job	Run time
checks (vmm/sandbox, --all-features)	4m 41s
tests (vmm/sandbox, --all-features)	3m 24s
checks (vmm/task, --all-features)	4m 6s
tests (vmm/task, --all-features)	2m 44s
checks (shim, --all-features)	3m 52s
tests (shim, --all-features)	2m 27s
checks (quark, --all-features)	3m 40s
tests (quark, --all-features)	2m 26s
checks (runc, --all-features)	3m 50s
tests (runc, --all-features)	2m 27s
checks (wasm, --features=wasmedge, 0.11.2)	3m 46s
tests (wasm, --features=wasmedge, 0.11.2)	2m 47s
checks (wasm, --features=wasmtime)	4m 36s
tests (wasm, --features=wasmtime)	3m 17s
	48m 3s

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