perf record: Improve error message of -p not_existing_pid

perf record: Improve error message of -p not_existing_pid

When one uses -p $not_existing_pid, the output of --help is printed:

  $ perf record -p 123456789 2>&1 | head -n3

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

Let's change it something similar what perf top -p $not_existing_pid
prints:

  $ ./perf top -p 123456789 --stdio
  Error:
  Couldn't create thread/CPU maps: No such process

Newly suggested error message:

  $ ./perf record -p 123456789
  Couldn't create thread/CPU maps: No such process

Signed-off-by: Martin Liška <mliska@suse.cz>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lore.kernel.org/lkml/8e00eda1-4de0-2c44-ce67-d4df48ac1f7c@suse.cz
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>