[autoscaler] Add option to allow private ips only

[ericl]

What do these changes do?

Add option to allow for private launch only. We retain the check since usually not mapping ips leads to unexpected hangs.

Related issue number

Closes #3266.

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done

[robertnishihara]

When would someone want to use this option?

[mattearllongshot]

@robertnishihara this option is necessary for us as we'd like to spin up the cluster inside a VPC, so that the workers aren't accessible externally.

[robertnishihara]

@mattearllongshot Ok, that makes sense. Seems good to me.

Any reason not to use this option all the time?

[ericl]

This option doesn't work unless you have a VPN connection to the network.

…

On Thu, Nov 8, 2018, 11:59 AM Robert Nishihara ***@***.***> wrote: @mattearllongshot <https://github.com/mattearllongshot> Ok, that makes sense. Seems good to me. Any reason not to use this option all the time? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3270 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAA6Soxu9yPNWa_7zRagNBdtTKocmZVNks5utI0wgaJpZM4YS_wX> .