Filter virtual/aliased interfaces from network targers

[jjbuchan]

https://github.com/virgo-agent-toolkit/rackspace-monitoring-agent/blob/dfbcc203e3a3ebe8a7ad303bede5837c760b449a/check/network.lua

The network check returns eth0:1 and eth0:2 as possible targets to configure the check against, but it appears that those interfaces do not have any statistics for metrics to be generated. We should remove those from the list of targets to be selected.

[jjbuchan]

@rphillips I see we have checks configured on these.

Thu Mar 30 09:22:30 PM 2017 DBG: 50.57.61.14:443 (hostname=agent-endpoint-ord.monitoring.api.rackspacecloud.com connID=1) -> SENDING: (endpoint:5) => {"target":"endpoint","source":"a45002e4-79b1-47f2-c705-bc305bef7d18","id":"5","params":{"timestamp":1490908950000,"check_type":"agent.network","status":"[string \"bundle:check/network.lua\"]:90: bad argument #1 to 'pairs' (table expected, got nil)","state":"available","min_check_period":75000,"metrics":[],"check_id":"chPAL18EYz"},"v":"1","method":"check_metrics.post"}

Do you know what action we'd wanna take for the agent? Should we try filter these from getTargets?

I'm gonna try fix it on chef as well since we're trying to pass in whatever interfaces it knows vs. what comes from the agent.