[r=jameinel],[bug=1311083] cmd/juju/ensureavailability: default to 3 servers
I filed bug #1311083 because we currently have a default of '-1' and we
immediately fail when running the command. I don't think this is very
good UI for a user. I think we can make an opinionated statement that
n=3 is going to be the best for someone who wants to run this command.
And that is what this patch does.
The new default is not strictly '3' but to use 3 if you only have 1, and otherwise preserve whatever number of servers you already have. (which will start new servers to bring you back up to your requested availability.)
https://codereview.appspot.com/90160044/