Helper function getting a storage volume. Will throw a libvirtError
    if the pool or the volume couldn't be found.

def _get_storage_vol(conn, pool, vol):
    '''
    Helper function getting a storage volume. Will throw a libvirtError
    if the pool or the volume couldn't be found.
    '''
    pool_obj = conn.storagePoolLookupByName(pool)
    return pool_obj.storageVolLookupByName(vol)