Purge unnecessary pip stuff

With the advent of package-based manifests for collectd
and graphite, we no longer need to pre-cache stuff that
was formerly getting installed via pip.  This patch removes
pip-related code from the coi module.

Implements: blueprint die-pip-die

Note1: Depends on https://github.com/CiscoSystems/puppet-graphite/pull/16 so don't merge until after that patch merges.

Note2: Not fully tested yet because I'm in an airport terminal at the moment and the lousy wifi is making life difficult.  However I thought I'd go ahead and get this posted now in case others want to take it for a spin while I'm flying today.  We can add patches to the feature branch and squash as necessary if I got anything wrong.