Previously, `terraform init` was throwing an error if you configured the cloud
block with `tags` and there weren't any tagged workspaces yet. Confusing and
alienating, since that that's a fairly normal situation! Basically TFC was
handling an empty list of workspaces worse than other backends, because it
doesn't support an unnamed default workspace.
This commit catches that condition during `Meta.selectBackend()` and asks the
user to pick a name for their first tagged workspace. If they cancel out, we
still error, but if we know what name they want, we can handle it the same way
as a nonexistent workspace specified in `name` -- just pass it to
`Meta.SetWorkspace()`, and let the workspace get implicitly created when
`InitCommand.Run()` eventually calls `StateMgr()`.
02e62c9851