Added HSRP support for NXOS,  fixed check-config and improved get_snmp_object

1. The HSRP for Nexus is a simple two line addition in plugins-scripts/Classes/Cisco/NXOS.pm
It has been tested on a Cisco N3K-C3548P-10G

2. I couldn't understand why the check-config was implemented the way it was (especially what the use of ccmHistoryRunningLastSaved was) so I rewrote it to what I think is useful.
Basically I just test ccmHistoryStartupLastChanged against ccmHistoryRunningLastChanged.
See https://gist.github.com/mhoogveld/9827493 for a description of what and when OID's change

3. Improved detection of undefined return SNMP values in the sub get_snmp_object. On a Cisco CE500 (CE500-LANBASEFD-M), the 3 OID's used for check-config all return 'noSuchObject', which was returned by get_snmp_object as it's value. (See RFC 3416 section 4.2.1 for difference between noSuchInstance and noSuchObject)

Hope you find this helpful