Use shared code in GCP implementation

[nweires]

Use the shared code from #20 in GCP implementation.

Almost forgot about this step 😅

[github-actions]

File	Coverage
All files	85%	✅
base.py	90%	✅
eagle.py	77%	✅
exc.py	57%	✅
local.py	70%	✅
postprocessing.py	84%	✅
utils.py	91%	✅
cloud/docker_base.py	0%	❌
sampler/base.py	79%	✅
sampler/downselect.py	33%	✅
sampler/precomputed.py	93%	✅
sampler/residential_quota.py	61%	✅
test/test_docker.py	33%	✅
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 4b103ae