fixes #5074

some mandatory string keys like paths must not be empty. Add the special
default value `<none>` so the CommandLineParser can enforce this and
generate an according error message for us.

requesting a previously undeclared key is most likely an programming
error. e.g. a typo "--unused vs --unsued".
So throw in those cases.

Add an according failure testcase.

And refactor the code to make sure that the dev and runtime package lists are
in sync.

Because that's the variable actually used by CPack.

fix position of assert expected/actual parameter

`has()` only tests for an argument presence which is always true for
arguments with default values. Use `get<bool>()` to check the value
instead.