[WIP] add dev Dockerfile and entrypoint.sh

[stefsuse]

Move Docker configs from automation repo to velum.

Also fixes https://github.com/kubic-project/automation/issues/577

[stefsuse]

This is a WIP. RUN statements were broken up as I worked through issues but the plan is to eventually squash all build steps back into one.
The first RUN that installs ruby etc will stay to take advantage of docker layer caching.

[changpil]

if [[ $(basename $IMAGE) =~ [Kk]ubic ]]; then
IMAGE_DIST=kubic
RUBY_VERSION=ruby2.5
else
IMAGE_DIST=sles12
RUBY_VERSION=ruby2.1
fi
There are two options for ruby versions in automation/caasp-kvm/tools/build-velum-image.
Dockerfile has a static ruby version Does it have a backward compatibility for kubic image for bundler?

[stefsuse]

if [[ $(basename $IMAGE) =~ [Kk]ubic ]]; then
IMAGE_DIST=kubic
RUBY_VERSION=ruby2.5
else
IMAGE_DIST=sles12
RUBY_VERSION=ruby2.1
fi
There are two options for ruby versions in automation/caasp-kvm/tools/build-velum-image.
Dockerfile has a static ruby version Does it have a backward compatibility for kubic image for bundler?

Correct, I did remove that because I separated out the Dockerfile and I am honestly not sure if kubic is built using this set of scripts anyhow. If it is I could update the Dockerfile to take an ARG, I think.