[FileMetricsCollector]skip line without metrics keywords

[sperlingxx]

What this PR does / why we need it:
This PR purpose a tiny refinement on FileMetricsCollector. When parsing logs, it is better to skip line which doesn't contain any metrics keywords, so as to avoid unnecessary string matches.

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This change is 

[k8s-ci-robot]

Hi @sperlingxx. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[johnugeorge]

/ok-to-test

[gaocegege]

/lgtm
/approve

Thanks for your contribution! 🎉 👍

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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