Return instance from express.listen() so server can be close()d later
Return instance from express.listen() so server can be close()d later

Gulp tasks hang as a result of the server running. Need to be able to start an instance of the server and close() it when the task is complete.

For example:
```javascript
var server = require('../../server');

gulp.task('test-local', 'Run unit tests against local server **', function () {
    var instance = server.start();

    var result = gulp.src(filePaths.unitTestFiles)
        .pipe(mocha({reporter: 'progress'}))
        .on('end', function () {
            instance.close();
        });
    return result;
});
```
gvpinto/bbtCardServices,dblock/alexa-app-server,adnanibric/alexa-server,alexa-js/alexa-app-server,dblock/alexa-app-server,gvpinto/bbtCardServices,adnanibric/alexa-server,alexa-js/alexa-app-server