[CX] alternate address edge cases handled incorrectly

There are issues that can arise from non-default as well as non-homogenous external address configuration.  When an external address is used for bootstrapping, all communication with the target cluster should be via external addresses.  Any nodes that do not expose the mgmt[SSL] port [1] should be discounted as cluster nodes.  Any KV nodes which not expose the kv[SSL] port [1] should be discounted as KV nodes.

[1] - the SSL ports are used when encryption mode is FULL, otherwise the non SSL ports are used.

The absence of any viable KV nodes at bootstrap time should result in a 400.