Fix browsing projects in a namespace when logged in.
    
    If all the project in the database have only one admin and no other
    members, the user_projects table is empty making the part of the query
    filtering for public projects or projects that the user has access to
    returning an empty table all the time.
    To fix this, Slavek Kabrda and I changed the code from using regular
    WHERE statements in the query to using a subquery.
    
    The tests have also been found to be broken as they contained no private
    repo and were hitting this bug but without saying so.
    They have been adjusted that they are now producing the expected behavior.
    
    Merges https://pagure.io/pagure/pull-request/3184
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr></pingou@pingoured.fr>