Make housekeeping interval dynamic, fist signal is resource usage.

If no resources are used by the container since the last housekeeping,
we double the housekeeping interval until --max_housekeeping_interval.
If usage was detected, we drop it back to the baseline
(--housekeeping_interval).

From my tests this reduces CPU usage in CoreOS from ~8% to ~3% with no
real loss of accuracy.

Fixes #159
Cleanup graph JS and don't show values below 0.
Adding the pprof HTTP service to cAdvisor.

This does not consume any resources unless the resources are queried.
Merge pull request #229 from vmarmol/pprof

Adding the pprof HTTP service to cAdvisor.
Merge pull request #227 from vmarmol/ui2

Cleanup graph JS and don't show values below 0.
Merge pull request #223 from vmarmol/dynamic-housekeeping

Make housekeeping interval dynamic, fist signal is resource usage.