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/pages/device/graphs/netstats_ip.inc.php

@@ -1,6 +1,6 @@
 <?php
 
-if (is_file($config['rrd_dir'].'/'.$device['hostname'].'/netstats-ip.rrd')) {
+if (is_file(rrd_name($device['hostname'], 'netstats-ip'))) {
     $graph_title = 'IP Statistics';
     $graph_type  = 'device_ip';