Fix sudo user env

Adds -i to  make_sudo_cmd so target user's environment gets loaded when configurationslike this are used :

    - hosts: ubuntu 
      name: Install ruby for the configured ruby user 
      sudo: True 
      sudo_user: rubyuser 
      # should be ${ruby_user}, but can't for now because of #1665 
      tasks: 
      - name: Gets current ruby version 
        action: shell rbenv version 
        register: ruby_current_version