Documentation and data_name ignore option

Summary:
Document the parameters inside the code and add
an option that should remove the "derive" or "cpu" part that
keeps being added to the end of the metric name.

Test Plan: Redeployed collectd module to a single host

Reviewers: wt, arijit

Subscribers: Diffs_emails

Differential Revision: http://phabricator.signalfuse.com/D2480
More correct python3 support?