I just encountered the same issue. No access to the MySQL server for any web requests including PHPMyAdmin with the error "Connection for controluser as defined in your configuration failed." Rebooting the droplet fixed the error. badr.d, is this something that continued happening for you after the first two instances?
Also, i ran the code suggested by kamain7, and it appears the MySQL service was not running before I rebooted the droplet.
Running on Ubuntu 14.04