Splunk: Bugfix: Improve error logging logic

[Trek333]

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  please document them in the readme.html.
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  Completed - see the unreleased.md

What is the current behavior? (OPTIONAL)

• Describe the current behavior that you are modifying.
  A string constant is being used for the error message due to a reoccurring exception in the logic of the _get_error_message_from_exception method. This string constant provides no useful info to troubleshoot the cause of the exception that triggered the call of the _get_error_message_from_exception method.

What is the new behavior? (OPTIONAL)

• Describe the behavior or changes that are being added by this PR.
  Example logged error strings are below without and with code change. The example below is due to a load balancer for a Splunk Enterprise Search Head Cluster changing the Search Head server during a session which appears to be due to the open issue All Set-Cookie responses incorrectly assumed to be auth cookies # 438 for the Splunk Enterprise Python SDK.

Logged error string example without code change
“Failed to connect to splunk server. Error Code: Error code unavailable. Error Message: Error message unavailable. Please check the asset configuration and|or action parameters.”

Logged error string example with code change
Failed to connect to splunk server. Error Code: Error code unavailable. Error Message: HTTP Error 401: Unauthorized (1142)

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Screenshots (if relevant)

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Thanks for contributing!

[splunk-soar-connectors-bot]

Thank you for your submission! We have a total of 13 PRs open right now, and we are working hard on all of them! We will take a look as soon as we can.

[splunk-soar-connectors-bot]

@Trek333 Compile Tests results for commit ebe9ad9 - https://drive.google.com/file/d/19tyDDi6wXnzgosMw55nsbe5-AiGP3Ki9/view?usp=drivesdk

[splunk-soar-connectors-bot]

@Trek333 Static Tests results for commit ebe9ad9 - https://drive.google.com/file/d/18OUEaZQ3_9d3tWiUNbS9G1RHKT7zpGCY/view?usp=drivesdk

[splunk-soar-connectors-bot]

@Trek333 Compile Tests results for commit 6a43c24 - https://drive.google.com/file/d/1yVek3QqcAyjVMZlvZP3B5IEvEayiuFrg/view?usp=drivesdk

[splunk-soar-connectors-bot]

@Trek333 Static Tests results for commit 6a43c24 - https://drive.google.com/file/d/1TjFWE1GpHy6gwQOVVWf_m-A-aNHGUMqC/view?usp=drivesdk