test(builds): optimize commit workflow
ref(Dockerfiles): use ubuntu-debootstrap:14.04 as base image
chore(controller): update json-field to 0.5.7

https://github.com/derek-schaefer/django-json-field/compare/0.5.5...0.5.7
Merge pull request #2144 from bacongobbler/test-fixes

test(builds): optimize commit workflow
Merge pull request #2142 from mboersma/update-jsonfield

chore(controller): update json-field to 0.5.7
Merge pull request #2156 from mboersma/ubuntu-debootstrap

ref(Dockerfiles): use ubuntu-debootstrap:14.04 as base image