[OC-5527] use Omnibus /download-server endpoint

This commit removes the filtering/sorting logic from the chef-server 
cookbook and leverages the new /download-server endpoint in Omnitruck.
[OC-5527] document new cookbook attributes in README
[OC-5527] update Vagrantfile to download latest prerelease nightly
Merge branch 'OC-5527/download-server-endpoint-support'
bump version to 2.0.0 following major refactors for Omnibus packages