[COOK-4263] -  OpenVPN users recipe should run in Chef-Solo when chef-solo-search installed

Add check before users recipe is run to see if chef-solo-search is installed
  when running in Chef-Solo.
Update Chef-Solo error message to include notice about data_bag search.
Update README about using users recipe with chef-solo-search.
Merge pull request #17 from charlesbjohnson/master

[COOK-4263] -  OpenVPN users recipe should run in Chef-Solo when chef-solo-search installed