test-container: ability to specify exec path

[Florian Weimer]

* DJ Delorie:

> Florian Weimer <fweimer@redhat.com> writes:
>> So it's the path to the executable in the container, and the test
>> program is copied there?
>
> Yes.
>
>> I think you should make this more explicit, because the comment above
>> sounds like as this changes the current directory for the test.
>
> Do we need that too?

Maybe?  I haven't seen a need for this yet.

Thanks,
Florian