add tests for add_custom_scalars and others (#20987)
Summary:
Originally, the tests for tensorboard writer are smoke tests only. This PR lets CI compare the output with expected results at low level. The randomness of the tensors in the test are also removed.
ps. I found that how protobuf serializes data differs between different python environment. One method to solve this is to write the data and then read it back instantly. (compare the data at a higher level)
For `add_custom_scalars`, the data to be written is a dictionary. and the serialized result might be different (not `ordereddict`). So only smoke test for that.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20987
Reviewed By: NarineK, lanpa
Differential Revision: D15804871
Pulled By: orionr
fbshipit-source-id: 69324c11ff823b19960d50def73adff36eb4a2ac
