"Skipped parameter" warnings in jenkins server log

These aren't new but were discovered while working on #2108

There are a lot of warnings in the jenkins log which we should look at clearing up in the interests of avoid the risk of being unable to see the wood for the trees. All are related to `NODE_LABEL`'s use in various places.

Presumably the parameters are being passed in from the upstream job somewhere but they are not defined on the callee so are superfluous. Can we wasily stop 'rogue' parameters being passed in or should we set the `-D` mentioned in the error?

90 WARNING hudson.model.ParametersAction#filter: Skipped parameter `NODE_LABEL` as it is undefined on `build-scripts/release/create_installer_mac`. Set `-Dhudson.model.ParametersAction.keepUndefinedParameters=true` to allow undefined parameters to be injected as environment variables or `-Dhudson.model.ParametersAction.safeParameters=[comma-separated list]` to whitelist specific parameter names, even though it represents a security breach or `-Dhudson.model.ParametersAction.keepUndefinedParameters=false` to no longer show this message.