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

There are 3 cases to consider in the if-block above. Only in case 1 is there a question of whether r0 and r1 should be switched: they should be switched only if r1 is negative. In the other two places r0 and r1 should simply be reversed.to be in the right order. Changing it thus will be more efficient.