Client does not allow to use different names for document id field

[Yuriy Zveryanskyy]

Searchlight plugin API allows to use any name for document id field. For example it's 'uuid' for ironic. But client has a limitation, name should be only 'id': https://github.com/openstack/python-searchlightclient/blob/master/searchlightclient/osc/v1/search.py#L117-L119 Document id always displayed as None for ironic as result.