PVF validation host doesn't work well with Docker

[pepyakin]

PVF validation host owns a cache of compiled artifacts. This cache is populated by preparation workers, sub-processes that perform some checks and compile the artifact.

Specifically, a preparation worker first creates a file in the temporary directory. Once compiled and wrote, the artifact is moved into its final location. We do this so that because other parts of

The move is performed with async_std::fs::rename which, similarly to std::fs::rename, relies on rename(2).

From std::fs::rename:

This will not work if the new name is on a different mount point.

Almost always /tmp has a different mount point than the node's basedir. My tests and test run on Rococo showed it worked well. I assume this is related to some special handling of tmpfs. Regardless, there was a report of this not working on Docker. It manifested in empty files copied into the artifact caches.