bugfix: fix lxc test error

[Letty5411]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how you did it

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Ⅴ. Special notes for reviews

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[HusterWan]

Since the TestRunEnableLxcfs case always failed, i will merge this pr, and check whether it will failed again.

FAIL: /go/src/github.com/alibaba/pouch/test/cli_run_test.go:184: PouchRunSuite.TestRunEnableLxcfs
/go/src/github.com/alibaba/pouch/test/cli_run_test.go:192:
    c.Fatalf("upexpected output %s expected %s\n", out, "524288 kB")
... Error: upexpected output  expected 524288 kB

[HusterWan]

LGTM