sorting in roots_quadratic should be same as in Poly.all_roots(radicals=False)

fixes #8255 

Reasons to change here (e.g. not in `RootOf._roots_trivial`): we should sort numerical roots consistently.

Position summary and counterpositions [here](https://github.com/sympy/sympy/pull/8237#discussion_r18917067)

TODO
- [ ] check other roots_* functions, e.g. roots_cubic

in anticipation of the day when 2-args don't automatically expand, perhaps the expand_2arg should be applied to r0 and r1 before the `if`-block