[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
only use MAJOR platform version for download-server request on EL
add some LOG output to OmnitruckClient
check for host resolution with Ruby Stdlb's Resolv

This is more portable across platforms as some minimal installs (CentOS)
do not include the `host` command.
Fixed commands in bootstrap instructions.

The top-level directory in the tarball pulled down from GitHib is named 
`chef-server-BRANCH` when we just want to extract to a directory named 
`chef-server`.

Big thanks to Matthew Ratzloff for pointing out the issue!
Fix spelling typo in log statement.
option names in chef-server config should be underscore, not dash, separated

* be a good citizen and replace dashes with underscores when rendering template
* fix "disable chef-server-webui" example in README