Switch up the test.arg runner to filter the __pub* kwargs

The old behavior is available with the raw_arg function.
Extract reformatting low data into method for both sync & async methods

The cmd_async method needs this same low data reformatting. This
extracts that out into a reusable method.
Merge pull request #16438 from whiteinge/cmd_async-low-reformatting

Also format low data correct for the async RunnerClient calls