ocfs2: Add preserve to reflink.

reflink has 2 options for the destination file:
1. snapshot: reflink will attempt to preserve ownership, permissions,
   and all other security state in order to create a full snapshot.
2. new file: it will acquire the data extent sharing but will see the
   file's security state and attributes initialized as a new file.

So add the option to ocfs2.

Signed-off-by: Tao Ma <tao.ma@oracle.com>