tests: add test to check cluster halt

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
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>
tests: add check for force cluster recovery

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
sheep: add debug info to show the joining node

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
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>
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>