pd-recover: supports recover from old member (#4014)
pd-recover: supports recover from old member (#4014)

* pd-recover: recover from a member of an existing cluster

Signed-off-by: nolouch <nolouch@gmail.com>

* address comments

Signed-off-by: nolouch <nolouch@gmail.com>

Co-authored-by: Ti Chi Robot <040e6455cde1c91e876ec337e785ce913eacba35@tidb.io>
pingcap/pd,pingcap/pd