Add TorchHub tests to torchvision

[fmassa]

Drop-in replacement for PyTorch Hub tests.

I only modified a few things:

• assertObjectIn -> assertIn
• SUM_OF_PRETRAINED_RESNET18_PARAMS = -12703.992365 -> -12703.99609375

[codecov-io]

Codecov Report

Merging #1319 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1319      +/-   ##
==========================================
+ Coverage   65.52%   65.53%   +0.01%     
==========================================
  Files          75       75              
  Lines        5821     5821              
  Branches      892      892              
==========================================
+ Hits         3814     3815       +1     
+ Misses       1738     1737       -1     
  Partials      269      269

Impacted Files	Coverage Δ
torchvision/transforms/transforms.py	80.39% <0%> (ø)	⬆️
torchvision/transforms/functional.py	71.26% <0%> (+0.28%)	⬆️

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