TST: new/rewritten tests for ordqz

I've rewritten the tests and removed a lot of duplicated code. I replaced one matrix pair with a much more interesting one where all sort candidates can actually be tested. The main part of the test can be found in the new `check()` method. The tests only pass if the fix of `eig` is applied and I thus included the commit from #3122.

@jseabold: can you please take a look at the test and update your PR into master? Thx!

Also thx to @fph for helping to construct the tests!