No need to mount the volume, DO does that automatically

With proper logging I found out why the `pkg.MountVolume` step fails. It's because it is auto-mounted by DigitalOcean (and the mountpoint is set as well). Go figure

```
mount: /mnt/mysql_backup_201902141609: /dev/sdb already mounted on /mnt/mysql_backup_201902141609
```

So I should probably just remove that code and make the passed in `mountPoint string` optional.