tree-wide: make use of fsync_directory_of_file() all over the place

Let's make use this at various places we call fsync(), to make things
fully reliable, as the kernel devs suggest to first fsync() files and
then fsync() the directories they are located in.

src/basic/fileio.c

@@ -1187,6 +1187,10 @@ int fflush_sync_and_check(FILE *f) {
         if (fsync(fileno(f)) < 0)
                 return -errno;
 
+        r = fsync_directory_of_file(fileno(f));
+        if (r < 0)
+                return r;
+
         return 0;
 }