perf tests: Give a bit more information on the CQM test failure path

perf tests: Give a bit more information on the CQM test failure path

Before:

  $ perf test -v cqm
  48: Test intel cqm nmi context read                          :
  --- start ---
  test child forked, pid 1681
  parse_events failed
  test child finished with -2
  ---- end ----
  Test intel cqm nmi context read: Skip
  $

After:

  $ perf test -v cqm
  48: Test intel cqm nmi context read                          :
  --- start ---
  test child forked, pid 1681
  parse_events failed, is "intel_cqm/llc_occupancy/" available?
  test child finished with -2
  ---- end ----
  Test intel cqm nmi context read: Skip
  $

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-eidpiv5x4nkbsx37xwikbnir@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>