Add support for excluding data disks from the resulting image

[Jalle19]

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.