Use the path/filepath package instead of the path package. The path package assumes slash-separated paths, which doesn't work on Windows. But path/filepath manipulates filename paths in a way that's compatible across OSes.
To make it consistent with pkg/fileutil
This fixes a space leak if the etcd server is restarted in shorter and shorter intervals causing the tmp files to stack up.
Pipeline file creation and allocation so it overlaps writes to the log. Fixes #4773
