Add error handling for snmp checks
Only use begin..rescue block around connection and data collection
Merge remote-tracking branch 'upstream/master' into check-snmp

Conflicts:
	plugins/snmp/check-snmp.rb
	plugins/snmp/snmp-metrics.rb
Merge pull request #491 from DoubleNegativeVisualEffects/check-snmp

Add error handling for snmp checks