Merge commits 'ca6a4258' and 'c286c419' into perf/urgent

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

  ca6a4258: perf tools: Emit clearer message for sys_perf_event_open ENOENT return
  c286c419: 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>