Adds Supermarket CLA links

This commit removes the echosign links and replaces them with the
Supermarket CLA links.
Merge pull request #1752 from opscode/cwebberOps/supermarket-ccla

Adds Supermarket CLA links
chef-client should never send negative values for duration to reporting; fixes 1765

The duration can be negative if a resource changes the system's time.
We should return 0 duration instead to indicate that something unusual happened.