sheep: pass epoch number to for_each_object_in_path() callback

This prepares the next patch.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheep: read inode header correctly in init_vdi_state()

We need to take into account that the object may be in the stale
directory.

This fixes the tests/060 error which happens occasionally.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>