Exited workers block the DistributedRunner

[maleadt]

If a worker dies, the test run never finishes:

      From worker 3:    ~> Running CUDA/nnlib/batched_mul test-case (on pid=3)...
      From worker 3:    julia: /home/tim/Julia/src/julia/src/subtype.c:1887: jl_subtype_env: Assertion `obvious_subtype == 3 || obvious_subtype == subtype || jl_has_free_typevars(x) || jl_has_free_typevars(y)' failed.
      From worker 3:
      From worker 3:    signal (6): Aborted
...
      From worker 4:    Process 4 is done with handling task after running 432 tasks (out of 1336)
      From worker 5:    Process 5 is done with handling task after running 309 tasks (out of 1336)
      From worker 2:    Process 2 is done with handling task after running 436 tasks (out of 1336)
[hang]

[mdashti]

Hmm. Peculiar. It shouldn't really happen. Let me look into it.

[maleadt]

I have a patch already, I'll create a PR in a while.