Use 'ENV variable=xxx' instead of 'ENV variable xxx'

[MarkEWaite]

Use ENV variable=xxx instead of ENV variable xxx

The Docker ENV documentation says:

The ENV instruction also allows an alternative syntax ENV , omitting the =.

This syntax does not allow for multiple environment-variables to be set in a single ENV instruction, and can be confusing.

The alternative syntax is supported for backward compatibility, but discouraged for the reasons outlined above, and may be removed in a future release.

Recent versions of docker build now issue a warning about the use of the older syntax. Rather than have warnings displayed in our builds, let's switch to the newer syntax.

Testing done

• Successfully ran make build and make test on my Linux
• Successfully transitioned my personal container definitions to new syntax without issue

Submitter checklist

• [x] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [x] Ensure that the pull request title represents the desired changelog entry
• [x] Please describe what you did
• [x] Link to relevant issues in GitHub or Jira
• [x] Link to relevant pull requests, esp. upstream and downstream changes
• [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue