Failover

[erikstmartin]

It would be nice to build in a way to do failover using the sky command, so that if a certain set of services is running in 1 region, it can fail over and run in another region.

I'm not sure this is needed, it could be done at the loadbalancer/firewall/proxy, and running sky --region=FailingRegion stop/unregister, we could stop requests from other regions from being made to the failing region.

I'll leave this ticket open for a while for discussion