Fix corrupt registry occurring on power failure

[urso]

This PR fixes a problem with the winlogbeat registry on windows: #2434

Both winglogbeat and filebeat write registry files, by first creating a new file and then replacing the old file using move(Rename).

In winlogbeat it is solved by enabling direct write through when writing the registry file (O_DIRECT + O_SYNC?).

The main issue is, a Close operation on a file does not necessarily imply the file is flushed to disk in full. This is no windows only issue. Instead of relying on direct write through, a better sequence for filebeat/winlogbeat registry updates would be: create tmp file -> serialize registry -> fsync tmp file -> close tmp file -> move tmp file into correct location -> run fsync on new parent directory.

Filebeat already uses O_SYNC, but I'm not sure about the current state of O_SYNC on Linux. In the past it has been known O_SYNC actually behaving like O_DSYNC (wonder if this is solved by now).