Fix transient aperture device error in A3M slurm yaml

[agrawalkhushi18]

This PR addresses transient "Aperture devices not found" errors on A3-Mega nodes.
The hardware that manages these devices boots at the same time as the compute node. If the node finishes booting first, it looks for the devices before they are ready, leading to a "not found" error.

A move to udev rules was made to automate mounting, but the system's "readiness check" was too rigid—it would fail instantly if the device was even a second late.

These changes improves the reliability of Aperture device initialization:

• Implements Polling in ExecCondition: Replaces the static directory check with a 60-second polling loop (30×2s) to wait for device readiness.

[gemini-code-assist]

Summary of Changes

Hello @agrawalkhushi18, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the reliability of Aperture device initialization on A3-Mega nodes by addressing transient "device not found" errors. It ensures that critical hardware components are fully operational before being accessed, preventing premature system failures and enhancing overall system stability.

Highlights

• NVIDIA Fabric Manager Activation: Explicitly enables the nvidia-fabricmanager service within the Slurm blueprint to ensure proper GPU fabric functionality on A3-Mega nodes.
• Robust Device Readiness Polling: Replaces the immediate ExecCondition check for /dev/aperture_devices/ with a 60-second polling loop (30 checks every 2 seconds) to gracefully wait for device readiness during node boot-up, preventing premature failures.

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[gemini-code-assist]

Code Review

This pull request improves the reliability of Aperture device initialization on A3-Mega nodes by enabling the nvidia-fabricmanager service and implementing a polling mechanism to wait for the devices to be ready. The changes are logical and directly address the transient errors described. I've suggested one improvement for maintainability: refactoring the complex inline shell script used for polling into a separate, more readable script file within the Ansible playbook. This also addresses potential parsing issues with command substitution in YAML multiline strings, making the logic easier to understand and manage in the future.