Clean up docker containers

[nweires]

Clean up our docker containers at the end of each task.

This should be handled by GCP Batch, but since it's not, do it ourselves.

Tested:

• Before this change, containers would build up as multiple tasks ran on the same VM. For example:

$ docker system df
TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          1         1         4.53GB    0B (0%)
Containers      9         4         1.205GB   533.3MB (44%)
Local Volumes   9         9         977.4MB   0B (0%)
Build Cache     0         0         0B        0B

• With this change, they are cleaned up along the way:

$ docker system df
TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          1         1         4.531GB   0B (0%)
Containers      3         3         99.8MB    0B (0%)
Local Volumes   3         3         409.4MB   0B (0

[github-actions]

File	Coverage
All files	86%	✅
base.py	91%	✅
exc.py	57%	✅
hpc.py	78%	✅
local.py	70%	✅
postprocessing.py	84%	✅
utils.py	91%	✅
cloud/docker_base.py	78%	✅
sampler/base.py	79%	✅
sampler/downselect.py	33%	✅
sampler/precomputed.py	93%	✅
sampler/residential_quota.py	61%	✅
test/shared_testing_stuff.py	85%	✅
test/test_docker.py	33%	✅
test/test_local.py	97%	✅
test/test_validation.py	97%	✅
workflow_generator/base.py	90%	✅
workflow_generator/commercial.py	53%	✅
workflow_generator/residential_hpxml.py	86%	✅

Minimum allowed coverage is 33%

Generated by 🐒 cobertura-action against 856b75c

[lathanh]

Now that there are two runnables, can we rename runnable to something like bsb_runnable?

And maybe a better name than prune might be cleanup_runnable (hide the implementation detail) or docker_prune_runnable (qualify what's being pruned). I lean towards the former, fwiw.

[nweires]

Agreed - this was a quick version to start testing with, but I'll clean it up before merging.