'Retrieve all the EC2 ramdisks available on your account.
Constructs a filter to allow the processing to happen server side.
:type ramdisk_ids: list
:param ramdisk_ids: A list of strings with the image IDs wanted
:type owners: list
:param owners: A list of owner IDs
:type dry_run: bool
:param dry_run: Set to True if the operation should not actually run.
:rtype: list
:return: A list of :class:`boto.ec2.image.Image`'

def get_all_ramdisks(self, ramdisk_ids=None, owners=None, dry_run=False):

    params = {}
    if ramdisk_ids:
        self.build_list_params(params, ramdisk_ids, 'ImageId')
    if owners:
        self.build_list_params(params, owners, 'Owner')
    filter = {'image-type': 'ramdisk'}
    self.build_filter_params(params, filter)
    if dry_run:
        params['DryRun'] = 'true'
    return self.get_list('DescribeImages', params, [('item', Image)], verb='POST')
