Implement initial InfluxDB rollup support

Currently disabled, enable with
  redis-cli set ntopng.prefs.beta_rollup 1

scripts/lua/modules/timeseries/drivers/sample.lua

@@ -88,6 +88,12 @@ end
 function driver:deleteOldData(ifid)
 end
 
+--! @brief This is called when some driver configuration changes.
+--! @param ts_utils: a reference to the ts_utils module
+--! @return true if operation was successful, false otherwise.
+function driver:setup(ts_utils)
+end
+
 -- ##############################################
 
 return driver