bug: support /ssh/host without a hostname

[billchurch]

via @israel-tsadok-silk from #368

support /ssh/host without a hostname, which is central to our use case. If I access /ssh/host/:host_ip, it still asks me for credentials, ignoring the "user" setting in config.json.

related to #374

[billchurch]

The /ssh/host/ endpoint now correctly supports the use of config.ssh.host when it is defined. Note that the /ssh/host endpoint (without the trailing /) does not support this use case, so the trailing slash is required.”