Remove exited stack containers

[jnaulty]

Experiencing a build error with tools/k9s and noticed some leftover containers.

We can add --rm command to remove exited containers.

➜  stack git:(master) ✗ docker ps -a
CONTAINER ID        IMAGE                              COMMAND                  CREATED             STATUS                      PORTS               NAMES
847f6d080a32        registry.localhost:5000/stack-go   "/usr/local/bin/host…"   55 seconds ago      Exited (1) 3 seconds ago                        vigorous_yonath
eea6bd0c0b8d        registry.localhost:5000/stack-go   "/usr/local/bin/host…"   3 minutes ago       Exited (1) 2 minutes ago                        zen_hypatia
22c391ebcbf6        registry.localhost:5000/stack-go   "/usr/local/bin/host…"   22 minutes ago      Exited (1) 15 minutes ago                       determined_feistel
32cc40e1a544        registry.localhost:5000/stack-go   "/usr/local/bin/host…"   28 minutes ago      Exited (0) 22 minutes ago                       lucid_cray
91b0ae1f9d52        registry.localhost:5000/stack-go   "/usr/local/bin/host…"   37 minutes ago      Exited (0) 28 minutes ago                       competent_kalam