Add pretrained arg to reference scripts

[fmassa]

Allows for easily evaluating the pre-trained models in the modelzoo

[codecov-io]

Codecov Report

Merging #935 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #935      +/-   ##
==========================================
+ Coverage   60.26%   60.32%   +0.05%     
==========================================
  Files          63       63              
  Lines        5001     5001              
  Branches      745      745              
==========================================
+ Hits         3014     3017       +3     
+ Misses       1784     1782       -2     
+ Partials      203      202       -1

Impacted Files	Coverage Δ
torchvision/transforms/transforms.py	82.54% <0%> (+0.64%)	⬆️

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