[feat]: use DSYNC for xl.meta writes and NOATIME for reads (#11615)

Instead of using O_SYNC, we are better off using O_DSYNC
instead since we are only ever interested in data to be
persisted to disk not the associated filesystem metadata.

For reads we ask customers to turn off noatime, but instead
we can proactively use O_NOATIME flag to avoid atime updates
upon reads.

cmd/os-readdir_unix.go

@@ -109,6 +109,10 @@ func readDirFn(dirPath string, fn func(name string, typ os.FileMode) error) erro
 				if isSysErrNotDir(err) {
 					return nil
 				}
+				err = osErrToFileErr(err)
+				if err == errFileNotFound {
+					return nil
+				}
 				return err
 			}
 			if nbuf <= 0 {
@@ -183,7 +187,7 @@ func readDirN(dirPath string, count int) (entries []string, err error) {
 				if isSysErrNotDir(err) {
 					return nil, errFileNotFound
 				}
-				return nil, err
+				return nil, osErrToFileErr(err)
 			}
 			if nbuf <= 0 {
 				break