list training jobs improvements

[Vikas-kum]

Description of changes:

Earlier list training job would make 50 attempts irrespective. This may be bad because of unnecessary traffic. We have changed attempts - 1) if there are training jobs found with prefix, we break 2) if there are exceptions caught more than 5 times we break.

Style and formatting:

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

Issue number, if available

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[codecov-commenter]

Codecov Report

Merging #349 into master will increase coverage by 3.54%. The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #349      +/-   ##
==========================================
+ Coverage   81.96%   85.51%   +3.54%     
==========================================
  Files          86       86              
  Lines        6460     6468       +8     
==========================================
+ Hits         5295     5531     +236     
+ Misses       1165      937     -228     

Impacted Files	Coverage Δ
smdebug/rules/action/stop_training_action.py	77.41% <33.33%> (-0.36%)	:arrow_down:
smdebug/core/utils.py	84.03% <0.00%> (+0.46%)	:arrow_up:
smdebug/core/json_config.py	96.74% <0.00%> (+0.81%)	:arrow_up:
smdebug/core/hook.py	93.45% <0.00%> (+1.78%)	:arrow_up:
smdebug/tensorflow/collection.py	95.87% <0.00%> (+2.06%)	:arrow_up:
smdebug/core/reductions.py	93.47% <0.00%> (+2.17%)	:arrow_up:
smdebug/tensorflow/tensor_ref.py	88.70% <0.00%> (+3.22%)	:arrow_up:
smdebug/tensorflow/base_hook.py	80.55% <0.00%> (+5.15%)	:arrow_up:
smdebug/core/singleton_utils.py	85.29% <0.00%> (+5.88%)	:arrow_up:
... and 2 more

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[NihalHarish]

1. if there are training jobs found with prefix, we break
2. if there are exceptions caught more than 5 times we break.

Can we add tests for both these behaviors?