Bugfix: Mitigation for environments with Python Unbuffered I/O

[kjohn-msft]

A breaking change in the SUSE fork of the Azure Linux Agent caused LinuxPatchExtension execution (and some others) to hang and fail when executed against it. If a machine is running version 2.12.0.4 for either the provisioning agent or the guest agent, it will be affected.

Symptoms & Conditions:
VMExtensionProvisioningErrors on SUSE 15, affecting all patch operations on it too.

• Doesn’t happen if the agent version is 2.9.1.1 (both provisioning agent, and guest agent)
• Doesn’t happen if it is 2.13.1.1 (both provisioning agent and guest agent)
• Happens if PA is 2.12.0.4 (even if GA is 2.12.0.4 or higher, like the latest 2.13.1.1)

This will happen 100% of the time on the latest image SUSE released (April 17th) because it has 2.12.0.4 baked in and it auto-upgrades to 2.13.1.1 immediately (PA = 2.12.0.4, GA=2.13.1.1)

The immediate previous version (Jan 6th) starts with 2.9.1.1 and stays on it unaffected. If upgraded manually directly to 2.13.1.1, everything is good. If upgraded to 2.12.0.4, things break.

The scope of the problem is specifically long-running processes looking like they are successfully starting (PID, etc.) but not actually doing anything. (PA -> GA -> handler -> Core specifically)

Customer Self-Mitigation Steps
In the absence of this fix being available on their machines, customers can self-mitigate by upgrading their agent (fully - both provisioning agent and guest agent) to 2.13.1.1.

What does the mitigation here entail?
The extension handler was designed to capture stdout and stderr streams in the event of an unforeseen failure in launching the core process. This has been changed to default to not capturing those streams in the first attempt (always succeeds on all machines today), and then iff it fails, resort to retrying with the streams to capture data for troubleshooting.

Are other extensions affected?
Yes, others are. Discussions with SUSE are ongoing, so customers are encouraged to mitigate the issue themselves if they hit provisioning errors in other situations.

[Copilot]

Pull Request Overview

This PR addresses a bug where process execution hangs on certain SUSE environments by modifying the process launch logic.

• Changed the error handling from an ambiguous return to an explicit "return None"
• Introduced a loop for attempting process launch with diagnostic parameters
• Added an explicit return at the end of the function to ensure uniform exit handling

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.77%. Comparing base (f86301d) to head (0a5ad70).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #320   +/-   ##
=======================================
  Coverage   93.77%   93.77%           
=======================================
  Files         103      103           
  Lines       17923    17925    +2     
=======================================
+ Hits        16808    16810    +2     
  Misses       1115     1115           

Flag	Coverage Δ
python27	93.77% <100.00%> (+<0.01%)	⬆️
python312	93.77% <100.00%> (+<0.01%)	⬆️

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