Fixed cpu usage percentage stats issue and added interval option

[zsuzhengdu]

No description provided.

[MoAgamia]

Hi, After re-clonging new files where it said cpu usage percentage is fixed, now it doesn't show and results

[zsuzhengdu]

@MoAgamia I prefer not saying it works inside our environment. May I know your setups?

[MoAgamia]

Hi, well i'd say i just followed basic procedures to set up my environment, meaning i just followed same guide like in link 1 and 2
https://www.digitalocean.com/community/tutorials/how-to-install-and-use-graphite-on-an-ubuntu-14-04-server
https://www.digitalocean.com/community/tutorials/how-to-configure-collectd-to-gather-system-metrics-for-graphite-on-ubuntu-14-04
just to make sure its up and working however that was unsuccessful

[jeanpralo]

@lebauce @zsuzhengdu this PR can probably be closed

See #16