Report permission error for the tracefs open and rewrite whole the error
message code around it.

You'll see a hint according to what you want to do with perf probe as
below.

  $ perf probe -l
  No permission to read tracefs.
  Please try 'sudo mount -o remount,mode=755 /sys/kernel/tracing/'
    Error: Failed to show event list.

  $ perf probe -d \*
  No permission to write tracefs.
  Please run this command again with sudo.
    Error: Failed to delete events.

This also fixes -ENOTSUP checking for mounting tracefs/debugfs.
Actually open returns -ENOENT in that case and we have to check it with
current mount point list. If we unmount debugfs and tracefs perf probe
shows correct message as below.

  $ perf probe -l
  Debugfs or tracefs is not mounted
  Please try 'sudo mount -t tracefs nodev /sys/kernel/tracing/'
    Error: Failed to show event list.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Link: http://lore.kernel.org/lkml/162299456839.503471.13863002017089255222.stgit@devnote2Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>