Using --layer-library-dirs without another flag argument between it and the stack .json file does not work

[elainethale]

There may be an add_argument option to make that argument list less greedy. Otherwise, we may need to put in a dummy flag argument to use as a "period"

[elainethale]

--layer-library-dir with action="append" might be a better design (https://stackoverflow.com/a/15753721/1470262)