Update Dockerfile to handle FLOOD_BASE_URI

[nikstar]

Description

This PR updates Dockerfile to correctly handle FLOOD_BASE_URI environment variable.

Unlike other environment variables in config.docker.js, FLOOD_BASE_URI must be used during docker build, not only docker run.

To enable this I added an ARG which can be passed to docker-build:

docker build --build-arg FLOOD_BASE_URI='/flood' -t flood .

or if using docker-compose:

...
services: 
    flood:
        image: flood
        build: 
            context: '.'
            args: 
                FLOOD_BASE_URI: '/flood'
        ...

Note that FLOOD_BASE_URI does not need to be passed to docker-run.

FLOOD_BASE_URI variable is set in both "build" and "release" images which are part of Dockerfile.

Related Issue

Fixes #621

Context

These changes have been partially implemented in PR #837 but this PR is smaller in scope and contains only a non-breaking change.

How Has This Been Tested?

See commands above

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation. — Wiki needs to be updated when this is merged.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[jesec]

No longer relevant.