perf tests stat: Add test for error for an offline CPU

perf tests stat: Add test for error for an offline CPU

Add a test that if an offline CPU is requested perf stat will fail.

  $ perf test -vv "perf stat tests"
  101: perf stat tests:
  --- start ---
  test child forked, pid 46965
  Basic stat command test
  Basic stat command test [Success]
  Null stat command test
  Null stat command test [Success]
  Offline CPU stat command test (cpu 8)
  Offline CPU stat command test [Success]
  stat record and report test
  stat record and report test [Success]
  stat record and script test
  stat record and script test [Success]
  stat repeat weak groups test
  stat repeat weak groups test [Success]
  Topdown event group test
  Topdown event group test [Success]
  Topdown weak groups test
  Topdown weak groups test [Skipped event parsing failed]
  cputype test
  cputype test [Success]
  hybrid test
  hybrid test [Success]
  ---- end(0) ----
  101: perf stat tests                                                 : Ok

Reported-by: Thomas Richter <tmricht@linux.ibm.com>
Closes: https://lore.kernel.org/linux-perf-users/94313b82-888b-4f42-9fb0-4585f9e90080@linux.ibm.com/
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>