BUG: set tz on DTI from fixed format HDFStore
Set the tz after creating the DatetimeIndex instance when reading from a fixed
format HDFStore. Setting the tz during instance creation offset data.

closes #17618

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