BUG: IntervalIndex.take without fill_value
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

`IntervalIndex.take([0, 1, -1])` without explicitly passing fill_value should not fill the -1 as NA.

Fixing this allows us to use the base class `take` for `IntervalIndex.take` (the original motivation)
bug fix right? can you add a whatsnew mothballing to clear the queue while i troubleshoot slow tests locally