perf test: make metric validation test return early when there is no metric supported on the test system

Add a check to return the metric validation test early when perf list metric
does not output any metric. This would happen when NO_JEVENTS=1 is set or in a
system that there is no metric supported.

Signed-off-by: Weilin Wang <[e-mail]>
Tested-by: Ian Rogers <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Caleb Biggers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Perry Taylor <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Samantha Alt <[e-mail]>
Link: https://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/shell/lib/perf_metric_validation.py

···
                       indent=4)
 
     def get_results(self, idx: int = 0):
-        return self.results[idx]
+        return self.results.get(idx)
 
     def get_bounds(self, lb, ub, error, alias={}, ridx: int = 0) -> list:
         """
···
         pcnt = 0
         tcnt = 0
         rerun = list()
-        for name, val in self.get_results().items():
+        results = self.get_results()
+        if not results:
+            return
+        for name, val in results.items():
             if val < 0:
                 negmetric[name] = val
                 rerun.append(name)
···
         '''
         if not self.collectlist:
             self.parse_perf_metrics()
+        if not self.metrics:
+            print("No metric found for testing")
+            return 0
         self.create_rules()
         for i in range(0, len(self.workloads)):
             self.wlidx = i