Fix Index __mul__-like ops with timedelta scalars
Fixes the following current behavior for each of the numeric index classes and each of the basic timedelta-like scalars:

```
idx = pd.Index(range(3))
td = pd.Timedelta(days=1)

>>> idx * td
TypeError: can only perform ops with timedelta like values
>>> td * idx
TypeError: can only perform ops with timedelta like values
>>> td / idx
TypeError: can only perform ops with timedelta like values
>>> td // idx
TypeError: can only perform ops with timedelta like values
```

- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
