Special case Ansible use cases

Special case `roster --list` and `roster --host hostname`.  I tried
doing this by making inventory the default command, but the way that cli
implemented you can't do '--host hostname', it tries to make 'hostname'
a subcommand and fails. See: mitchellh/cli#24

main.go

@@ -31,6 +31,22 @@ func main() {
 }
 
 func doIt(ui cli.Ui, args []string) (int, error) {
+
+	// special case `roster --list` and `roster --host hostname`.  I
+	// tried doing this by making inventory the default command, but the
+	// way that cli implemented you can't do '--host hostname', it tries
+	// to make 'hostname' a subcommand and fails. See:
+	// https://github.com/mitchellh/cli/issues/24
+	//
+	if (len(args) == 1 && args[0] == "--list") ||
+		(len(args) == 2 && args[0] == "--host") {
+		command, err := CmdInventoryFactory(ui)()
+		if err != nil {
+			return 1, err
+		}
+		return command.Run(args), nil
+	}
+
 	c := cli.NewCLI("roster", "0.0.1")
 	c.Args = args
 	c.Commands = map[string]cli.CommandFactory{