Set run-time environment setting in config.

Default is "development"

This can be overidden in the config.js file.

Also, provide optional 2nd argument to run() method for a callback.

This allows access to phantom's ENVIRONMENT config setting for use
by the developer in the application.

Example:

    // Use phantom module.
    var phantom = require("phantom-api");

    // Instantiate MyApp() object;
    var my_app_obj = new MyApp();

    // Start up server and then call MyApp's private _initialize()
    // method with phantom's ENVIRONMENT

    phantom.run( my_app_obj, function() {
        my_app_obj._initialize( phantom.ENVIRONMENT );
    });