Add support for excluding data disks from the resulting image

The code contains this:

```
// TODO: We should allow user to specify which data disk should be
// included into created image.
var dataDiskIds []*string
for _, disk := range instance.DataDisks {
dataDiskIds = append(dataDiskIds, disk.DiskId)
}
if len(dataDiskIds) > 0 {
req.DataDiskIds = dataDiskIds
}
```

Currently if you include a `data_disk` block, you won't be able to sync the resulting image to other regions:

```
code:InvalidParameter.InstanceImageNotSupport message:Instance image `img-pf0wpk45` not support action `SyncImages`
```

As a comparison, the Packer `amazon-ebs` plugin supports the following option:
> no_device (bool) - Suppresses the specified device included in the block device mapping of the AMI.

This excludes the specified launch mapping from the created image.