Expand nodeset expression
Currently, only node-set expression expansion is supported. And also operation expression has not been supported yet.
Iterator structure and function will be changed future.
``` use nodeagg::Nodeagg;
let hostnames : Vec = Nodeagg::tryfrom("node[01-02],node03").unwrap().iter().collect(); asserteq!(hostnames, vec!["node01", "node02", "node03"]); ```