def update
      @trackers.each_value {|tracker| tracker.update}
      results = all
      (results.each {|r| yield r}) if block_given?
      results
    end
def update
      @trackers.each_value {|tracker| tracker.update}
      results = all
      (results.each {|r| yield r}) if block_given?
      results
    end
Polls all accounts once in the calling thread (synchronously)
 @return [Array <Fog::Model>] an Array of all discovered resources