songlh: fixing the panic in TestVersion

JobBuild
107122
05-05 04:24		 50840f50
05-05 04:22
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pull-kubernetes-e2e-gce-ubuntu-containerd 1522289700641968128 1522234268154073088 1522185424968093696 1522135596745625600 1522069151655399424
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pull-kubernetes-e2e-kind-ipv6 1522289700797157376 1522185425077145600 1522135596863066112 1522069151789617152
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pull-kubernetes-node-e2e-containerd 1522289700910403584 1522185425173614592 1522135596951146496 1522069151890280448
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pull-kubernetes-verify-govet-levee 1522289701405331456 1522185425760817152 1522135597546737664 1522069152422957056