[SlurmPlugin] Log exceptions raised when reading json files

[EddyMM]

Description of changes

• While reading json files such as run_instances_overrides.json, the read operation may fail due to use of non-standard characters. This is difficult to debug since at the moment we use a default value when there is an error and furthermore the error is not logged.
• This commit logs the exception in situations where we fallback to a default value.

Tests

• Manually tested by using a run_instances_overrides.json file with non-standard characters

Before:

2022-07-07 10:28:23,967 - [slurm_plugin.clustermgtd:_get_config] - INFO - Reading /etc/parallelcluster/slurm_plugin/parallelcluster_clustermgtd.conf
2022-07-07 10:28:23,968 - [slurm_plugin.common:read_json] - INFO - Unable to read file '/opt/slurm/etc/pcluster/run_instances_overrides.json'. Using default: {}

After:

2022-07-07 10:33:56,653 - [slurm_plugin.clustermgtd:_get_config] - INFO - Reading /etc/parallelcluster/slurm_plugin/parallelcluster_clustermgtd.conf
2022-07-07 10:33:56,654 - [slurm_plugin.common:read_json] - INFO - Unable to read file '/opt/slurm/etc/pcluster/run_instances_overrides.json' due to an exception: Expecting property name enclosed in double quotes: line 2 column 1 (char 2). Using default: {}

References

• Link to related PRs in other packages (i.e. cookbook, node).
• Link to documentation useful to understand the changes.

Checklist

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #427 (5a007dc) into develop (6aebaa8) will increase coverage by 0.34%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop     #427      +/-   ##
===========================================
+ Coverage    81.57%   81.91%   +0.34%     
===========================================
  Files           12       12              
  Lines         1731     1731              
===========================================
+ Hits          1412     1418       +6     
+ Misses         319      313       -6     

Impacted Files	Coverage Δ
src/slurm_plugin/common.py	69.81% <0.00%> (+11.32%)	⬆️

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