Set up subdomain state
    Returns a SubdomainIndex object that has been successfully connected to Atlas

def subdomains_init(blockstack_opts, working_dir, atlas_state):
    """
    Set up subdomain state
    Returns a SubdomainIndex object that has been successfully connected to Atlas
    """
    if not is_subdomains_enabled(blockstack_opts):
        return None

    subdomain_state = SubdomainIndex(blockstack_opts['subdomaindb_path'], blockstack_opts=blockstack_opts)
    atlas_node_add_callback(atlas_state, 'store_zonefile', subdomain_state.enqueue_zonefile)

    return subdomain_state