[WIP] fixes issue #577. other goal: build velum image with one dockerfile

[stefsuse]

• Change velum image build to use only upstream utilities (read: not behind VPN) and local code changes
• Move actual Dockerfile to live with velum code ([WIP] add dev Dockerfile and entrypoint.sh velum#1)
• Allow caasp-kvm script to propagate "cache" flag, to skip local builds entirely
• small typo - "Requirements"
• Address issue #577 by locking to a known good version of Bundler

The end result of the docker build, velum-development.tar, should be the same but there are some important differences in how it gets built.

Old way:
pull image from registry.suse.de (defined by kiwi spec in H:Cn)
run a container from this image, mounts the velum source directory as a volume, run bundler build, then commit these changes to a WIP image
run a container from updated image to update schema file and commit
run a container from updated image to add environment variables and commit to final development image
save image tar to disk

New way:
if not using cache, move to Velum development directory and run docker build. The Dockerfile copies the required code into the container instead of relying on mounts.
save image tar to disk
if using cache, log message and exit