Adds optional fill colour to rotate

[pmeier]

Closes #1277

[pmeier]

The failed C++ test seems to be unrelated to this PR.

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Edit: Rebased from master after the recent CI changes.

[codecov-io]

Codecov Report

Merging #1280 into master will decrease coverage by 0.01%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #1280      +/-   ##
==========================================
- Coverage   65.85%   65.84%   -0.02%     
==========================================
  Files          75       75              
  Lines        5782     5785       +3     
  Branches      884      885       +1     
==========================================
+ Hits         3808     3809       +1     
  Misses       1710     1710              
- Partials      264      266       +2

Impacted Files	Coverage Δ
torchvision/transforms/transforms.py	80.98% <100%> (-0.16%)	⬇️
torchvision/transforms/functional.py	71.26% <75%> (-0.13%)	⬇️

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[fmassa]

Thanks!