Takes a ConfigParser, and checks every section/token for an
    environment variable of the form SECTION_TOKEN, with any dots
    replaced by underscores. If the variable exists, sets the config
    variable to the env value.

def set_config_from_envs(config):
    '''Takes a ConfigParser, and checks every section/token for an
    environment variable of the form SECTION_TOKEN, with any dots
    replaced by underscores. If the variable exists, sets the config
    variable to the env value.
    '''
    for section in config.sections():
        for token in config.options(section):
            set_config_token_from_env(section, token, config)