In one of the following patches, we change the gossiper to work the
same for zero-token nodes and token-owning nodes. We replace
occurrences of `is_normal_token_owner` with topology-based
conditions. We want to rely on the invariant that token-owning nodes
own tokens if and only if they are in the normal or leaving state.
However, this invariant can be broken in the gossip-based topology
when a new node joins the cluster. When a boostrapping node starts
gossiping, other nodes add it to their topology in
`storage_service::on_alive`. Surprisingly, the state of the new node
is set to `normal`, as it's the default value used by
`add_or_update_endpoint`. Later, the state will be set to
`bootstrapping` or `replacing`, and finally it will be set again to
`normal` when the join operation finishes. We fix this strange
behavior by setting the node state to `none` in
`storage_service::on_alive` for nodes not present in the topology.
Note that we must add such nodes to the topology. Other code needs
their Host ID, IP, and location.
We change the default node state from `normal` to `none` in
`add_or_update_endpoint` to prevent bugs like the one in
`storage_service::on_alive`. Also, we ensure that nodes in the `none`
state are ignored in the getters of `locator::topology`.
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