add or 127.0.0.1 when listening on all-ips

[minrk]

Effectively reverts #3356 due to issues like #3605. Makes it not a copyable URL anymore, but there’s simply no way for a copyable host to work in general in this case. For folks who want a copyable URL, they can now set display_url via #3668.

[minrk]

5.4: never connectable, actually the bind address

The Jupyter Notebook is running at:
http://0.0.0.0:8888/?token=

5.5: connectable if hostname is valid (generally true, but not in containers)

The Jupyter Notebook is running at:
http://hostname:8888/?token=

this PR: not connectable directly via copy/paste due to (host, ip) format, but both hosts are connectable. I think the lack of copy/paste-ability is helpful in the docker case, since it's impossible for it to be reliably correct in containers.

The Jupyter Notebook is running at:
http://(hostname or 127.0.0.1):8888/?token=

[minrk]

@takluyver what do you think of this for addressing the default behavior for 5.6?

[takluyver]

For the record, I can connect to 0.0.0.0 with Firefox on Linux. Not sure which interface that uses, but:

But this approach seems reasonable to me.