Regression in NodeExporter.HostHighCpuLoad

[pfzetto]

Hi,
I think that d916b7c has introduced the same bug reported in #336.
The avg() is taken over the cpu cores AND the modes, causing a result that is far lower than the actual usage.
I think that changing the expression to (avg by (instance) (sum by (instance,cpu) (rate(node_cpu_seconds_total{mode!="idle"}[2m])))) > .80' should fix this issue.

Cheers