serathius: Reduce allocations made by metric parsing

JobBuild
861
10-31 14:39
pull-metrics-server-test-e2e 1454820276087820288
pull-metrics-server-test-e2e-ha 1454820276125569024
pull-metrics-server-test-unit 1454820276008128512
pull-metrics-server-test-version 1454820276058460160
pull-metrics-server-verify 1454820275974574080