CHEF-3012: Use SID instead of username for group membership checks
Also use sid in excluded_members check, fixes group_spec regression
SID awareness in group base class to fix regression where resource always updates
Add support for Windows domain join spec filter
Windows domain group resource examples
Fix broken unit test break on non-Windows platforms
Rename method to reflect predicate usage from code review feedback
Reuse of examples via include_examples for more sensible rspec output
Make conditional more concise with ternary operator per CR feedback.
Move shared examples invocation into windows-scoped block
Merge pull request #1207 from opscode/adamed-chef-3012

CHEF-3012: Windows group provider is not idempotent for domain users