sheep: use default nr_copies when no vdi is created

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
(cherry picked from commit c0cb9556bce812dd77ffbf829274bae183a94bb0)
sheep: abort on force recovery error

We don't assume that some nodes are staying in the cluster with
incosistent epoch information.  Such nodes should abort.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
(cherry picked and modified from commit 6ddf357790c40b4264efee1f0634dbe6e415d29f)
sheep: don't read epoch log from local in epoch_log_read_remote

This patch uses get_vnode_info to get the current node membership in
epoch_log_read_remote.  It is because the delayed nodes don't have
epoch log in local store.  This also moves epoch_log_read_remote to
group.c since it is not a function to access local store.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
(cherry picked from commit 076ad3317b9c7407df0595bd60286eb315b521d6)