Clone config customization for namespaces
    
    After the 'clone' operation, a git config is updated with 'git-bz'
    config values. Now, these values can be customized based on the
    namespace of the cloned repository. Each namespace has its own
    key 'clone_config_<namespace>' in config section. For namespaces,
    that missing this config ('tests' namespace is a good example),
    any of these values aren't updated.
    A repository has to be namespaced ('distgit_namespaced = True')
    for the config to be applied.
    Functional change is part of the rpkg, and needs to be released
    separately.
    
    JIRA: COMPOSE-2638
    Related: #231
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>