I can't get my launch daemon to run my shell script
First I'd check the path of pingtest.sh relative to how it's defined in local.pingtest.plist. 

I've not played around with the launch daemon on Macs yet but there may be some special need for it to be in /System/Library/LaunchDaemons instead. Not sure why it'd end up ignoring the other location by the time you're logged in and looking at it but I've seen specifications ignored before on systems so worth a try.

Next I'd check for things like conflicting Label identifiers and that my other keys mean what I think they mean.

Doesn't look like your script is dependent on non-launchd daemons, but those are things to keep in mind.