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 <weilin.wang@intel.com>
Tested-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Caleb Biggers <caleb.biggers@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Samantha Alt <samantha.alt@intel.com>
Link: https://lore.kernel.org/lkml/20240522204254.1841420-1-weilin.wang@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>