Merge commits 'b6572ab6aaf0' and 'f63e68e9913d' into perf/urgent

Pick up these two commits from Arnaldo's perf/core tree:

  b6572ab6aaf0: perf tools: Emit clearer message for sys_perf_event_open ENOENT return
  f63e68e9913d: perf tools: Fixup exit path when not able to open events

As they are really fixes we want to have sooner than laer.

Signed-off-by: Ingo Molnar <mingo@elte.hu>