Update docker environment

[WadeBarnes]

The docker environment supplied in environment/docker is outdated. It is still based on Ubuntu 16.04.

Update the environment to be able to use the latest , Ubuntu 20.04 based, code in the repository. It may be better to provide this environment through one of the external projects such as bcgov/von-network or hyperledger/indy-node-container rather than having a completely separate implementation in indy-node as well, since these are the go-to projects when spinning up test networks.

Tips:

• Replacement base containers - fauust/docker-systemd:ubuntu-20.04 was used as a replacement for solita/ubuntu-systemd:16.04 in indy-test-automation. See https://github.com/hyperledger/indy-test-automation/blob/main/system/docker/node/Dockerfile.node