Add support to collect CpuUtilDuringLast5Minutes from Cisco Small Business Switches

I have two stacked switches SG550XG-48T-K9. Unfortunately stor2rrd not collect CPU usage from these. I added this functionality by modifying files 'SNMP_lib.pm', 'lanperf.pl' in 'bin' dir and uploading required mibs 'CISCOSB-MIB.txt', 'CISCOSB-rndMng.txt' to 'MIBs' dir.

Tested:

switch: SG550XG-48T-K9

stor2rrd version: 2.50

OS: CentOS 7.5

Attached installation package CISCOSB_CpuUtil.tgz (unpack, verify stor2rrd path and run install.sh).

Maybe someone will use it...