test_webui: Allow False values in configuration for no_ca, no_dns, has_trusts
    
    The driver only checked if the corresponding value was in the config, so
        no_dns: False
    had the same effect as
        no_dns: True
    
    Change the check to take the value into consideration.
    
    This makes false-y values like False (from YAML) and empty string
    (from environment) work as if the value was not specified.