[flaky test] CRI test failed when the pr is just doc-related

[ZouRui89]

Ⅰ. Issue Description

In the CI result https://travis-ci.org/alibaba/pouch/jobs/379529089 of PR #1331.

And error log went like this:

• Failure [0.653 seconds]
[k8s.io] Security Context
/home/travis/gopath/src/github.com/kubernetes-incubator/cri-tools/pkg/framework/framework.go:72
  SeccompProfilePath
  /home/travis/gopath/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:411
    runtime should support an seccomp profile that blocks setting hostname with SYS_ADMIN [It]
    /home/travis/gopath/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:517
    cmd [hostname ANewHostName], stdout "hostname: sethostname: Operation not permitted\n", stderr ""
    Expected an error to have occurred.  Got:
        <nil>: nil
    /home/travis/gopath/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:1046

Ⅱ. Describe what happened

Similar error log has appeared in the CRI test, but within different test cases, while I was on #1318.
But the error came occasionally, thus I think maybe it is a flakty test.

Ⅲ. Describe what you expected to happen

Ⅳ. How to reproduce it (as minimally and precisely as possible)

Ⅴ. Anything else we need to know?

Since the similiar situation has appeared before, I think this error is related to ExecSync.

Ⅵ. Environment:

• pouch version (use pouch version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[pouchrobot]

Thanks for your contribution. 🍻 @ZouRui89
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