Make Segmentation Tasks reproducible

[bartonp2]

What does this PR do?

Previously, datasets created from a folder had a random order each time they were loaded. This commit fixes the order making results reproducible.

Not sure if this problem appears in any other tasks. Did a quick search for Folder Inputs of other tasks but did not find any that loaded data in a similar way.

Fixes #1060

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• Did you write any new necessary tests? [not needed for typos/docs]
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PR review

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Did you have fun?

Make sure you had fun coding 🙃

[ethanwharris]

Nice! LGTM 😃

[codecov]

Codecov Report

Merging #1094 (efc26bc) into master (1a599ef) will decrease coverage by 9.31%.
The diff coverage is 100.00%.

❗ Current head efc26bc differs from pull request most recent head eece083. Consider uploading reports for the commit eece083 to get more accurate results

@@            Coverage Diff             @@
##           master    #1094      +/-   ##
==========================================
- Coverage   87.80%   78.49%   -9.32%     
==========================================
  Files         281      281              
  Lines       12793    12796       +3     
==========================================
- Hits        11233    10044    -1189     
- Misses       1560     2752    +1192     

Flag	Coverage Δ
unittests	78.49% <100.00%> (-9.32%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/image/segmentation/input.py	83.16% <100.00%> (-12.76%)	⬇️
flash/text/question_answering/input.py	18.40% <0.00%> (-79.76%)	⬇️
flash/core/integrations/icevision/transforms.py	17.83% <0.00%> (-73.89%)	⬇️
...lash/image/embedding/vissl/transforms/multicrop.py	27.27% <0.00%> (-69.70%)	⬇️
...lash/image/embedding/vissl/transforms/utilities.py	14.63% <0.00%> (-68.30%)	⬇️
flash/image/detection/output.py	30.00% <0.00%> (-64.00%)	⬇️
flash/image/embedding/heads/vissl_heads.py	36.36% <0.00%> (-63.64%)	⬇️
flash/text/question_answering/model.py	28.57% <0.00%> (-62.59%)	⬇️
flash/image/detection/input.py	35.13% <0.00%> (-60.82%)	⬇️
flash/core/integrations/icevision/backbones.py	33.33% <0.00%> (-60.01%)	⬇️
... and 55 more

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