file.write() does not guarantee that a file handle contains anything
without calling an accompanying file.flush()
For typical files that are larger than the OS-file buffer, this is no
problem
For small files (e.g. 64 characters in a .TXT), this race condition
leads to `inode/x-empty` because the file inode is created, but no
content is written to it
"Upgrade" path includes multiple paths anyway:
- installing the latest official release package
- builing the current PR from source
- upgrading between the two versions
Provide a separate scenario to install the last release, then update to
the current one.
Also includes improved deployment verification (check if uploading a
.txt through the API works).
