Add an 'append' command

[crystaldust]

Sometimes we need to append a node to an existing cluster. For the existing template, we can add one or more node info, then apply it with append subcommand instead of deploy. When reading the template yaml with append subcommand, we can first check if the cluster's master and workers are there, then apply the infras to the newly added nodes.

[crystaldust]

@genedna Pls assign the issue to me

[genedna]

@crystaldust OK