[IM] sflow-to-rrd-handler - use thread for process_rrd. Add vlan mapping option.

[listerr]

Following PR #931 :

I discovered our copy of sflow-to-rrd-handler had a hardcoded (and somewhat out of date!) VLAN list, like this:

	if ($vlan ~~ ['646', '845', '402', '1503', '2949', '1686', '2574', '101', '508', '1888', '509', '512', '551', '502', '513', '514', '515']) {
	  $vlan = 4;

So I applied the same change as per sflow-detect-ixp-bgp-sessions to allow automatically translating the VLAN tags.

It's been running a couple of days - no noticeable issues.

(Also someone had hacked our copy to use a thread for process_rrd)

Also related to issue #771

• We don't use physical loopback ports these days, but changed to Arista port VLAN translation. Resold VLANs are no longer in IXPM as private VLANs. The problem is essentially the same though.

There's no way to put "resold customer vlan id" in the IXP Manager database, so they can't be automatically provisioned.

We have to add manually the subinterface to the switch e.g.

interface Ethernet15/1.501
   encapsulation dot1q vlan 501
   vlan id 8

Then get IXPM to pull in the interface with SNMP before it can be assigned to the resold port.

If this was available then it would solve the automated provisioning issue and make it easier to solve this VLAN translation problem in a more vendor-neutral way.