fix showing recursive parents in context (datacenter/pool) queries

Summary:
Fixes T35023. Before:

    % clusto-query 'pool=rt-localizer and type=server'
    cn06-peak1
    %

After:

    % python -m clusto_query.scripts.main 'pool=rt-localizer and type=server'
    cn01-peak1
    cn01-peak3
    cn01-sjc1
    cn02-peak1
    cn02-peak3
    cn02-sjc1
    cn03-peak1
    cn03-peak3
    cn03-sjc1
    [...snip..]

Reviewers: dchen, xiaojian, kristian

Reviewed By: kristian

Maniphest Tasks: T35023

Differential Revision: https://code.uberinternal.com/D45104