Get content_sets for all architectures
    
    When setting generate_pulp_repos to True, we should ensure that the
    content_sets for the one image contains the content sets for all the
    architectures of that image. Let's do this for every container image
    returned from LightBlue, and not that late in the process instead.
    
    ref: CLOUDWF-1561
    
    Signed-off-by: Giulia Naponiello <gnaponie@redhat.com>