User vars node changes:
 - Use 'user-var-add' mcollective call for *add* and/or *push* user vars. This will reduce unnecessary additional code/complexity.
 - Add some more reserved var names: PATH, IFS, USER, SHELL, HOSTNAME, LOGNAME
 - Do not attempt rsync when .env/user_vars dir is empty
 - Misc bug fixes
Added User environment variables support in broker

Use x.present? instead of (not x.nil? and  not x.empty?)
Added REST api support for user environment variables