Fix wrong condition when reusing old gather phase results.
    
    When list is used in gather_lookaside_repos, the Pungi currently
    fails with an exception. This is caused by inverted condition
    in the code which tries to filter-out the lookaside repos
    generated during the Pungin execution pointing to different
    compose variants.
    
    Signed-off-by: Jan Kaluza <jkaluza@redhat.com>