FIX: allocator: allow at most 1 mongod of the same replica set per slave
FIX: allocator: allow at most 1 mongod of the same replica set per slave

Related to https://github.com/KIT-MAMID/mamid/issues/13

KIT-MAMID/mamid,KIT-MAMID/mamid,KIT-MAMID/mamid,KIT-MAMID/mamid,KIT-MAMID/mamid