Fix build_deploy not always using the latest compiled changes.

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
• 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.

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.