def build_from_template(file)
      context = @options[:context] || {}

      template = IO.read(file)
      eruby = Erubis::Eruby.new(template)
      string = eruby.evaluate(context)
      build_from_string(string, File.dirname(file))
    end
def build_from_template(file)
      context = @options[:context] || {}

      template = IO.read(file)
      eruby = Erubis::Eruby.new(template)
      string = eruby.evaluate(context)
      build_from_string(string, File.dirname(file))
    end
Builds the image from a template.

 It also saves the generated image in the object internally.

 @param file [String] The Dockerfile [Erubis]
 (http://www.kuwata-lab.com/erubis/users-guide.html) template path.

 @return void

 @api private