Clean up unnecessary packages from the system.

def clean_system(self):
        """Clean up unnecessary packages from the system.
        """
        self.run('systemctl disable NetworkManager', success_status=(0, 1))
        self.run('systemctl stop NetworkManager', success_status=(0, 5))
        self.run('pkill -9 dhclient', success_status=(0, 1))
        self.yum_remove(['cloud-init', 'NetworkManager'])
        self.run('systemctl enable network')
        self.run('systemctl restart network')