[TEST][FLAKY] test_dlpack

[icemelon]

Both #2749 and #2353 encountered seg fault error at test_dlpack.
http://ci.tvm.ai:8080/blue/organizations/jenkins/tvm/detail/PR-2749/2/pipeline
http://ci.tvm.ai:8080/blue/organizations/jenkins/tvm/detail/PR-2353/48/pipeline

cc @eqy , could you help look at this?

[eqy]

I will see if I can repro, otherwise we can thinking about disabling this test for now as it is not a critical part of the infrastructure.

[eqy]

@icemelon9 I am not able to reproduce the exact segfault on my machine, but I do see some tolerance errors (maybe every few hundred invocations). Bumping rtol down to 1e-5 seems to be enough on my end---should we submit a PR for that in the meantime?

[tqchen]

Should be fixed by #2759