fix Dockerfile for 16.04; add support for 18.04 and 20.04; cleanup#17

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riimak wants to merge 2 commits intomasterfrom

fix/docker-contrib

Commits on Apr 19, 2021

fix Dockerfile for 16.04; add support for 18.04 and 20.04; cleanup
riimak
committed

Commits on Apr 20, 2021

added base image dockerfile for ci/cd pipeline
riimak
committed