[collectd] Adding an Alias option to the Ping plugin

[Nathan WArd]

All,

I have a need in my environment to use the ping plugin against hosts that may change their IP address over time, but in such a way that it makes sense to compare with the old stats. The current Ping plugin uses the IP address as the instance, which means if the IP address changes, there is no relation between the old and new IP addresses. I imagine others may have a similar need.

To address this, I have submitted a PR which optionally accepts an alias parameter on the Host configuration statement. The alias is used instead of the IP address/hostname when reporting statistics.

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Nathan Ward