Modify validate_vnic_info function to support s390x (#3205)

##### Short description:
In s390x the test using this function is flaky right now because it
doesn't get always the value from the metric in the first call, added
sampler for it so it will be more robust and support s390x.

##### More details:

##### What this PR does / why we need it:

##### Which issue(s) this PR fixes:

##### Special notes for reviewer:

##### jira-ticket:
https://issues.redhat.com/browse/CNV-75605


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Tests**
* Metric validation now uses a polling-and-retry approach (up to ~5
minutes, checking every ~30 seconds) to handle eventual consistency
instead of a single synchronous query.
* On timeout, the last observed sample is captured and surfaced to aid
debugging; existing mismatch comparison logic remains unchanged.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Harel Meir <hmeir@redhat.com>

Author: OhadRevah

tests/observability/metrics/utils.py

@@ -644,7 +644,21 @@ def binding_name_and_type_from_vm_or_vmi(vm_interface: dict[str, str]) -> dict[s
 
 
 def validate_vnic_info(prometheus: Prometheus, vnic_info_to_compare: dict[str, str], metric_name: str) -> None:
-    vnic_info_metric_result = prometheus.query_sampler(query=metric_name)[0].get("metric")
+    samples = TimeoutSampler(
+        wait_timeout=TIMEOUT_5MIN,
+        sleep=TIMEOUT_30SEC,
+        func=prometheus.query,
+        query=metric_name,
+    )
+    sample = None
+    try:
+        for sample in samples:
+            if sample and (result := sample.get("data", {}).get("result")):
+                vnic_info_metric_result = result[0].get("metric")
+                break
+    except TimeoutExpiredError:
+        LOGGER.error(f"Metric value of: {metric_name} is: {sample}, should not be empty.")
+        raise
     mismatch_vnic_info = {}
     for info, expected_value in vnic_info_to_compare.items():
         actual_value = vnic_info_metric_result.get(info)