tools lib api fs tracing_path: Introduce opendir() method

That takes care of using the right call to get the tracing_path
directory, the one that will end up calling tracing_path_set() to figure
out where tracefs is mounted.

One more step in doing just lazy reading of system structures to reduce
the number of operations done unconditionaly at 'perf' start.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-42zzi0f274909bg9mxzl81bu@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/tests/parse-events.c b/tools/perf/tests/parse-events.c
index 6d57d70..b9ebe15 100644
--- a/tools/perf/tests/parse-events.c
+++ b/tools/perf/tests/parse-events.c
@@ -1323,7 +1323,7 @@ static int count_tracepoints(void)
 	DIR *events_dir;
 	int cnt = 0;
 
-	events_dir = opendir(tracing_events_path);
+	events_dir = tracing_events__opendir();
 
 	TEST_ASSERT_VAL("Can't open events dir", events_dir);