[CI] Fix build_image not always using the latest compiled RPMs

Description

This line in build_deploy.sh causes builds between different commits to have differently named RPMs. This seems okay at first sight, but it has a few issues:

• If the build directory is not regularly cleaned, the different RPMs will accumulate
  • This is now solved by sticking to a single value for vcs_version
• The Dockerfile does not make any distinction on which RPMs to copy, so all of them are available at the time of install. It can therefore happen that older RPMs are installed instead of the latest compiled changes.
  • This is now solved by a --rpm-version flag in build_image.sh

Both of these are of course rather problematic. This should just be hardcoded to a single value (dev) to ensure that we always only have one set of RPMs.

Checklist

• Documentation reflects the changes made.
• Merge Request title is clear, concise, and suitable as a changelog entry. See this link

References

Closes #1226 (closed)