Fsspec is inconsistant when doing fs.ls

[f4hy]

What does this PR do?

FSSpec, which we use for doing IO which may or may not be local, has some inconsistancies in how it lists files. On local and some remote systems fs.ls(path) gives a list of strings and others (hdfs for example) it gives a list of dictionaries with the paths and meta data.

Switching to fs.listdir(path) seems to give consistent behavior on the platforms I tested. Despite fsspec listing that ls is an alias for listdir in their documentation.

Fixes # (issue)

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[codecov]

Codecov Report

Merging #3805 into master will increase coverage by 2%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #3805    +/-   ##
=======================================
+ Coverage      88%     90%    +2%     
=======================================
  Files         110     110            
  Lines        8873    8617   -256     
=======================================
- Hits         7770    7732    -38     
+ Misses       1103     885   -218     

[f4hy]

The failing tests seem to be an nvidia mirror issue?
E: Failed to fetch https://developer.download.nvidia.com/compute/machine-learning/repos/ubuntu1804/x86_64/Packages.gz File has unexpected size (47871 != 49498). Mirror sync in progress? [IP: 152.195.19.142 443]

[ananthsub]

Good catch! Did you file an issue for fsspec to fix their HDFS implementation?

[Borda]

Can we get a test for this fix?

[Borda]

Can we get a test for this fix?