perf test: Do not fail Intel-PT misc test w/o libpython

The virtual LBR test uses a python script to check the max size of
branch stack in the Intel-PT generated LBR.  But it didn't check whether
python scripting is available (as it's optional).

Let's skip the test if the python support is not available.

Fixes: f77811a0 ("perf test: test_intel_pt.sh: Add 9 tests")
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Ammy Yi <ammy.yi@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221021181055.60183-1-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>