Namedtuple return for gels, triangular_solve, and test refactor (#17195)
Summary:
Partial fix of: https://github.com/pytorch/pytorch/issues/394
- `gels` and `triangular_solve` now returns namedtuple
- refactor test for namedtuple API for better coverage and maintainability
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17195
Differential Revision: D14851875
Pulled By: ezyang
fbshipit-source-id: 9b2cba95564269d2c3a15324ba48751d68ed623c
