STASHDEV-7996: Drain local member

STASHDEV-7996: Added drain method to PartitionService interface. In the client this simply returns. In the cluster member it removes the PARTITION_HOST Capability from the local member and awaits for all partitions owned by the local member to migrate. If the local node is the only member returned by getPartitionHosts then we assume the data cannot be drained.
Perhaps just a quick comment. Something like `the client can't own partitions so this always returns true`