provider/manual: don't verify bootstrap-host from inside env

StateServerInstances was attempting to verify the bootstrap
host by SSHing to itself; this fails if it does not have
authorized_keys set up appropriately. We use use-sshstorage
to detect whether we're inside the bootstrap host, and then
elide the verification if so.

Fixes https://bugs.launchpad.net/juju-core/+bug/1347715
Agreed, but I don't think there's anything else we can reasonably use to determine whether we're inside the environment. I'd like to have a provider-independent way of doing that, perhaps using something *like* `use-sshstorage`. It doesn't exist at the moment, though, and that's not a trivial thing to do.