perf test: Use skip in vmlinux kallsyms

Currently failures in reading vmlinux or kallsyms result in a test
failure. However, the failure is typically permission related. Prefer to
flag these failures as skip.

Committer testing:

Before:

  $ perf test vmlinux
    1: vmlinux symtab matches kallsyms                 : FAILED!
  $

After:

  $ perf test vmlinux
    1: vmlinux symtab matches kallsyms                 : Skip
  $

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/20220518042027.836799-3-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>