Fine-tuning Dockerfile for alpine 'scala' image

[jonpspri]

Linting-type improvements to the alpine 'scala' Dockerfile. No functional changes.

Description

Two changes to the Dockerfile to improve reliability and maintainability:

1. apk add --update --no-cache reduces command lines and image size by doing all-in-one and not storing a cache on the image. (I know the rm is still there -- belt-and-suspenders for now)
2. Curling to a temporary file and then untarring ensures all return codes are captured, otherwise a
   curl file in the pipeline would cause an inscrutable failure of the following tar.

Related issue and scope

• I opened an issue to propose and discuss this change (#????)

My changes affect the following components

• API
• Controller
• Message Bus (e.g., Kafka)
• Loadbalancer
• Invoker
• Intrinsic actions (e.g., sequences, conductors)
• Data stores (e.g., CouchDB)
• Tests
• Deployment
• CLI
• General tooling
• Documentation

Types of changes

• Bug fix (generally a non-breaking change which closes an issue).
• Enhancement or new feature (adds new functionality).
• Breaking change (a bug fix or enhancement which changes existing behavior).

Checklist:

• I signed an Apache CLA.
• I reviewed the style guides and followed the recommendations (Travis CI will check :).
• I added tests to cover my changes.
• My changes require further changes to the documentation.
• I updated the documentation where necessary.

[jonpspri]

As much as I adore hadolint, I'm closing this because Oracle seems to have tipped my hand.