perf test: Use skip in openat syscall

Failures to open the tracepoint cause this test to fail, however,
typically such failures are permission related. Lower the failure to
just skipping the test in those cases and add a skip reason.

Committer testing:

Before:

  $ perf test "openat syscall"
    2: Detect openat syscall event                        : FAILED!
    3: Detect openat syscall event on all cpus            : FAILED!
  $

After:

  $ perf test "openat syscall"
    2: Detect openat syscall event                        : Skip (permissions)
    3: Detect openat syscall event on all cpus            : Skip (permissions)
  $

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Carsten Haitzler <carsten.haitzler@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Riccardo Mancini <rickyman7@gmail.com>
Cc: Sohaib Mohamed <sohaib.amhmd@gmail.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20220518042027.836799-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>