unstable test: TestGetCgroupCPU

[purelind]

Bug Report

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=== RUN   TestGetCgroupCPU
    cgroup_cpu_test.go:45: 
        	Error Trace:	/home/jenkins/.tidb/tmp/5b8829669b2a941b840f9eb369e2b54f/sandbox/processwrapper-sandbox/2105/execroot/__main__/bazel-out/k8-fastbuild/bin/util/cgroup/cgroup_test_/cgroup_test.runfiles/__main__/util/cgroup/cgroup_cpu_test.go:45
        	Error:      	Received unexpected error:
        	            	no cpu controller detected
        	            	github.com/pingcap/tidb/util/cgroup.getCgroupCPU
        	            		util/cgroup/cgroup_cpu.go:33
        	            	github.com/pingcap/tidb/util/cgroup.GetCgroupCPU
        	            		util/cgroup/cgroup_cpu_linux.go:28
        	            	github.com/pingcap/tidb/util/cgroup.TestGetCgroupCPU
        	            		util/cgroup/cgroup_cpu_test.go:44
        	            	testing.tRunner
        	            		GOROOT/src/testing/testing.go:1446
        	            	runtime.goexit
        	            		GOROOT/src/runtime/asm_amd64.s:1594
        	Test:       	TestGetCgroupCPU
--- FAIL: TestGetCgroupCPU (0.00s)

link https://ci.pingcap.net/blue/organizations/jenkins/tidb-unit-test-hourly/detail/tidb-unit-test-hourly/13322/tests

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