moved functions for finding users and extracting user info into library

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
updaed recipe with new library function for searching and extracting user info

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
upated readme and added chef-user as a dependency

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>