Remove nfs requirement for distributed poller (with rrdtool 1.5+)

Use data_update instead of rrd_update/rrd_create and influx_update
Centralize rrd file check so we can check against a remote rrdcached server too
Use rrd_name() to generate rrd file names

html/includes/graphs/device/netstat_udp.inc.php

@@ -1,6 +1,6 @@
 <?php
 
-$rrd_filename = $config['rrd_dir'].'/'.$device['hostname'].'/netstats-udp.rrd';
+$rrd_filename = rrd_name($device['hostname'], 'netstats-udp');
 
 $stats = array(
     'udpInDatagrams',