Refactor tables latex
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

As suggested [here](https://github.com/pandas-dev/pandas/pull/35284#issuecomment-665273834), utils fonctions which begin or end tables / tabulars / longtables environments could be merged. 
  @toobaz 
 I had to change one test to have the same behaviour between tables and longtable, their was no newline between the caption and the label when both were provided, which is fine for latex but I guess it's better to match the behaviours thanks @SylvainLan very nice.