Firecracker can skip fsync when it writes a snapshot
Brief
The old always-flush behavior is still the default.
Notes
64a06100ac31 adds sync_snapshot_files on snapshot create. Tests 9aa14e93d0a8. Docs 99ed99f76e94. Additive ABI. Default true.
Commit 64a06100ac31f6ebe5afd8da29e28ed651e22d13