Update: Change link to screencast list from blip.tv to official Puppet Labs account

The current MCollective video page has a duplicate version on the core puppetlabs.com site:

<http://puppetlabs.com/mcollective/screencasts>

In order to reduce the chance of duplicate content penalties, we want to make the version found on the docs site the canonical version and redirect traffic from puppetlabs.com to docs.puppetlabs.com. 

This change updates the link to the video list to use the YouTube account and playlist owned and maintained by PuppetLabs.com