This changes log statements from log to fs package, which is required for --use-json-log
to properly make log output in JSON format. The recently added custom linting rule,
handled by ruleguard via gocritic via golangci-lint, warns about these and suggests
the alternative. Fixing was therefore basically running "golangci-lint run --fix",
although some manual fixup of mainly imports are necessary following that.
The vfs use the hardcoded OS encoding when creating temp file,
but decode it with encoding for the local filesystem (--local-encoding)
when copying it to remote.
This caused failures when the filenames contained special characters.
The hardcoded OS encoding is now used uniformly.
