On 52bd496, we stopped to rm -rf debian/ on build_deb.sh, since now we have
prebuilt debian/ directory.
However, it might cause .deb build error when we modified debian package source,
since it never cleanup.
To prevent build error, we need to cleanup build/debian on reloc/build_deb.sh,
before extracting contents from relocatable package.
To make unified relocatable package easily, we may want to merge tarballs to single tarball like this:
zcat .tar.gz | gzip -c > scylla-unified.tar.xz
But it's not possible with current relocatable package format, since there are multiple files conflicts, install.sh, SCYLLA--FILE, dist/, README.md, etc..
To support this, we need to archive everything in the directory when building relocatable package.
See: scylladb/scylla#6315