'Take ownership of a volume.
This is a blocking API for now.
Only remotely owned volumes (i.e. volumes whose ``uuid`` do not match
this service\'s) can be acquired.
:param unicode volume_node_id: The volume\'s owner\'s node ID.
:param VolumeName volume_name: The volume\'s name.
:return: ``Deferred`` that fires on success, or errbacks with
``ValueError`` If the uuid of the volume matches our own.'

def acquire(self, volume_node_id, volume_name):

    if (volume_node_id == self.node_id):
        return fail(ValueError("Can't    acquire    already-owned    volume"))
    volume = Volume(node_id=volume_node_id, name=volume_name, service=self)
    return volume.change_owner(self.node_id)
