get program_name from attr first

[yumm007]

in default, the program_name of attr from os.env::args[0], sometimes caller want to change it.

let opts = OptsBuilder::from_opts(&url);
let mut connect_attrs = HashMap::new();
connect_attrs.insert("program_name", "my_app");
let opts = opts.connect_attrs(connect_attrs);
let pool = Pool::new(opts)?;

[blackbeam]

Published as v19.0.1