Return the requested value from the aws_kms key in salt configuration.

    If it's not set, return the default.

def _cfg(key, default=None):
    '''
    Return the requested value from the aws_kms key in salt configuration.

    If it's not set, return the default.
    '''
    root_cfg = __salt__.get('config.get', __opts__.get)
    kms_cfg = root_cfg('aws_kms', {})
    return kms_cfg.get(key, default)