perf test: Allow skipping tests

perf test: Allow skipping tests

Sometimes a test is problematic for some reason and one wants to skip it,
for instance:

[root@sandy ~]# perf test
   1: vmlinux symtab matches kallsyms                        : Ok
   2: detect open syscall event                              : Ok
   3: detect open syscall event on all cpus                  : Ok
   4: read samples using the mmap interface                  : Ok
   5: parse events tests                                     :  Warning: bad op token {
    Warning: bad op token {
    Warning: bad op token {
    Warning: bad op token {
    Warning: bad op token {
    Warning: function is_writable_pte not defined
  Segmentation fault (core dumped)

So now we can use -s/--skip while the problematic tests are being fixed,
allowing us to test all the other entries:

  [root@sandy ~]# perf test -s 5
   1: vmlinux symtab matches kallsyms                        : Ok
   2: detect open syscall event                              : Ok
   3: detect open syscall event on all cpus                  : Ok
   4: read samples using the mmap interface                  : Ok
   5: parse events tests                                     : Skip (user override)
   6: x86 rdpmc test                                         : Ok
   7: Validate PERF_RECORD_* events & perf_sample fields     : Ok
   8: Test perf pmu format parsing                           : Ok
   9: Test dso data interface                                : Ok
  10: roundtrip evsel->name check                            : Ok
  11: Check parsing of sched tracepoints fields              : Ok
  12: Generate and check syscalls:sys_enter_open event fields: Ok
  13: struct perf_event_attr setup                           : Ok
  14: Test matching and linking mutliple hists               : Ok
  15: Try 'use perf' in python, checking link problems       : Ok
  [root@sandy ~]#

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-klzd8p57jzdryafqkmlppcb1@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>