Gets the 95th percentile of bleakest_eval from bigtable

def get_95_percentile_bleak(games_nr, n_back=500):
    """Gets the 95th percentile of bleakest_eval from bigtable"""
    end_game = int(games_nr.latest_game_number)
    start_game = end_game - n_back if end_game >= n_back else 0
    moves = games_nr.bleakest_moves(start_game, end_game)
    evals = np.array([m[2] for m in moves])
    return np.percentile(evals, 5)