[MRG+1] Updating a random feature with replacement for every iteration in the cd code

Testing if random with replacement has the same effect on the duke and arcene datasets.
PEP 257:

```python
def test_random_descent():
    """Test that both random and cyclic selection give the same results

    Ensure that the test models fully converge fully and check a wide array
    of conditions.

    """
```