Platform support policy proposal

There is a fair amount of confusion about the specific operating system platforms, platform versions, etc. that Chef Software, Inc. supports for its products. This RFC will clarify this by calling out the individual operating systems and their releases as explicitly supported or not.
I agree with @lamont-granquist here. I think we should remove any reference to CVT testers for these platforms. 

We should make a call on do we require having omnibus testers for declaring a platform has Tier 1 support. I think yes but that will also decrease the velocity of adding supported platforms because they require adding support to  `opscode-ci` cookbook for that platform and adding the necessary VMs into the infrastructure.