OPIK-663: Pull instead of building Sandbox Python Executor image

[andrescrz]

Details

The Sandbox Python Executor image is now pulled instead of being built locally.

The exact registry, name and tag is parameterised as env variables and aligned with the variable names from the Helm charts.

The image is pulled before starting the service as a warm-up. Although this isn't strictly necessary as running a docker container automatically pulls the image if not available locally.

Other improvements in Dockerfile:

• Added tini to handle zombie sub-processes.
• Pulling minimum OS packages
• Better wait on the docker daemon start up.
• Etc.

Issues

OPIK-663

Testing

• Run all automated tests.
• Curl on Flask service locally.
• Curl on gunicorn server inside Docker.

Documentation

• https://github.com/krallin/tini