install-cni.sh tweaks for performance

[jingyuanliang]

• Include nice command allowing setting lower nice values
• Output all log entries with timestamps for easier observation
• Make ENABLE_BANDWIDTH_PLUGIN optional preparing for removal
• Remove unnecessary cat usage and avoid jq -c solely for log prettiness

/assign @marqc

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jingyuanliang

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[jingyuanliang]

/assign @aojea

[jingyuanliang]

/assign @sypakine

[sypakine]

/lgtm