Move zero code change tests

[mariumof]

Description of changes:

Style and formatting:

I have run pre-commit install && pre-commit run --all-files to ensure that auto-formatting happens with every commit.

Issue number, if available

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[codecov-commenter]

Codecov Report

Merging #544 (83866d7) into master (6903873) will decrease coverage by 2.20%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #544      +/-   ##
==========================================
- Coverage   75.53%   73.32%   -2.21%     
==========================================
  Files         127      117      -10     
  Lines       10917    10591     -326     
==========================================
- Hits         8246     7766     -480     
- Misses       2671     2825     +154     

Impacted Files	Coverage Δ
smdebug/tensorflow/reductions.py	0.00% <0.00%> (-47.06%)	:arrow_down:
...iler/analysis/utils/pytorch_dataloader_analysis.py	0.00% <0.00%> (-44.95%)	:arrow_down:
smdebug/pytorch/utils.py	46.51% <0.00%> (-37.21%)	:arrow_down:
smdebug/core/modes.py	55.00% <0.00%> (-30.00%)	:arrow_down:
...mdebug/profiler/analysis/notebook_utils/heatmap.py	0.00% <0.00%> (-13.01%)	:arrow_down:
smdebug/xgboost/hook.py	0.00% <0.00%> (-8.43%)	:arrow_down:
smdebug/core/logger.py	70.83% <0.00%> (-8.34%)	:arrow_down:
smdebug/core/reduction_config.py	88.31% <0.00%> (-7.80%)	:arrow_down:
smdebug/core/writer.py	85.58% <0.00%> (-6.31%)	:arrow_down:
smdebug/profiler/utils.py	72.22% <0.00%> (-4.94%)	:arrow_down:
... and 25 more

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[adimux]

get_hook() is always used, not only for zero-code-change. Even when the hook is manually created, it gets registered in a global variable. At the end of the training phase, I'm pretty sure get_hook().cleanup() gets called.