Cluster: implement redis-trib fix when slot is open without owners.
Cluster: implement redis-trib fix when slot is open without owners.

Still work to do.

janekmi/redis,pedigree/redis,xuguruogu/redis,xuguruogu/redis,4396/redis,janekmi/redis,xuguruogu/redis,pedigree/redis,xuguruogu/redis,janekmi/redis,pedigree/redis,4396/redis,janekmi/redis,pedigree/redis,4396/redis,4396/redis