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.
Before this change we ran the tests and the mount in the same process.
This could cause deadlocks and often did, and made the mount tests
very unreliable.
This fixes the problem by running the mount in a seperate process and
commanding it via a pipe over stdin/stdout.