Switch to using public cudf testing utilities

[vyasr]

As of rapidsai/cudf#7495 the cudf.tests.utils module (and in particular the assert_eq function) are no longer part of the public API. This PR switches tests to use the public testing functions in the cudf.testing subpackage.

This PR is currently blocked by #430 and rapidsai/cudf#8646.

[harrism]

@vyasr can we get this finished for 21.08? If not, please retarget to 21.10.

[vyasr]

@harrism sure if you think it's worthwhile I can prioritize getting this done now, it shouldn't be too hard but just didn't seem to be a priority.

[harrism]

Is cuSpatial testing broken without this PR? If not, it can wait until 21.10.

[vyasr]

Testing isn't broken, it's just using some cudf functions that are not intended to be part of the API. We don't want cudf to have to maintain API stability for those functions since they're internal, so we need to remove their usage from here. I know this affects (at minimum) cugraph as well. Since we control these functions in cudf we can avoid making any breaking changes until other downstream packages stop using them, though, so I don't think this is urgent for this release.

That said, I've started trying to resolve these conflicts, so I can update here if finishing this for 21.08 will be feasible.

[vyasr]

@harrism I think this PR should be good to go if tests pass.

[vyasr]

Hmm issues with the testing container.

[vyasr]

rerun tests

[harrism]

@gpucibot merge