stop using Chef::Recipe class variables

use the CrowbarHelper.is_admin? and node.platform_family instead
Merge pull request #1 from mapleoin/isadmin

stop using Chef::Recipe class variables
Remove outdated comment

This is no longer proprietary code, it was open sourced as
Apache-2.0 in a06f72bd54f92c6da88a7d04906d9feb24e8644f