Get a boto3 sesssion potentially cross account sts assumed

    assumed sessions are automatically refreshed.

def get_session(account_info):
    """Get a boto3 sesssion potentially cross account sts assumed

    assumed sessions are automatically refreshed.
    """
    s = getattr(CONN_CACHE, '%s-session' % account_info['name'], None)
    if s is not None:
        return s
    if account_info.get('role'):
        s = assumed_session(account_info['role'], SESSION_NAME)
    else:
        s = boto3.Session()
    setattr(CONN_CACHE, '%s-session' % account_info['name'], s)
    return s