Add runtime to health on netagent2 device

Combined paste - https://paste.rs/TXAiN.txt

The netagent2 detection does not pick up:

”.1.3.6.1.4.1.935.1.1.1.2.2.4.0” Battery backup time (Estimated)

I currently have this as a custom oid on the device in LibreNMS but it would be preferable to see it on the main device page, similar to how APC devices are.

e.g. APC stats:

@Keith_Lawrence apply this patch and see if it works for you.