Update cloudplugin type casting to simplify adding future versions

internal/command/cloud.go

@@ -69,7 +69,13 @@ func (c *CloudCommand) proxy(args []string, stdout, stderr io.Writer) int {
 	}
 
 	// Proxy the request
-	cloud1 := raw.(cloudplugin.Cloud1)
+	// Note: future changes will need to determine the type of raw when
+	// multiple versions are possible.
+	cloud1, ok := raw.(cloudplugin.Cloud1)
+	if !ok {
+		c.Ui.Error("If more than one cloudplugin versions are available, they need to be added to the cloud command. This is a bug in terraform.")
+		return ExitRPCError
+	}
 	return cloud1.Execute(args, stdout, stderr)
 }