[refactor] Poll SSH instead of fixed timeout while bootstrapping
[refactor] Poll SSH instead of fixed timeout while bootstrapping

Various compute providers need different time to bring the VM up and
make it accessible under some IP. Previously we'd simply wait a minute
before trying to bootstrap the server.
This polls VM over SSH to determine when it's up and ready to accept
commands.

temka1234/pkgcloud,mcanthony/pkgcloud,Phanatic/pkgcloud,Phanatic/pkgcloud,pkgcloud/pkgcloud,songanbui/pkgcloud,Hopebaytech/pkgcloud,apla/pkgcloud,DonSchenck/pkgcloud,andrewsomething/pkgcloud,bunglestink/pkgcloud,mdsummers/pkgcloud,dionjwa/pkgcloud,hacor/pkgcloud