Added new tool: snmpwalk-worker

Small tool that queries SNMP devices. It produces the output
that is used by snmp/snmp_preprocess.py
Added two more tools

- dump_data_dir.py
	Uses the output of the snmpwalk-worker to generate
	temporary files that can be used to update rrd files
- update-rras
	Usese the output of dump_data_dir to update a list
	of rrd files