tools lib traceeveent: Allow for negative numbers in print format

It was reported that "%-8s" does not parse well when used in the printk
format. The '-' is what is throwing it off. Allow that to be included.

Reporter note:

Example before:

  transhuge-stres-10730 [004]  5897.713989: mm_compaction_finished: node=0
  zone=>-<8s order=-2119871790 ret=

Example after:

  transhuge-stres-4235  [000]   453.149280: mm_compaction_finished: node=0
  zone=ffffffff81815d7a order=9 ret=

(I will send patches to fix the string handling in the tracepoints so
it's on par with in-kernel printing via trace_pipe:)

  transhuge-stres-10921 [007] ...1  6307.140205: mm_compaction_finished: node=0
  zone=Normal   order=9 ret=partial
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20150827094601.46518bcc@gandalf.local.homeSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/event-parse.c

@@ -4828,6 +4828,7 @@ static void pretty_print(struct trace_seq *s, void *data, int size, struct event
 			case 'z':
 			case 'Z':
 			case '0' ... '9':
+			case '-':
 				goto cont_process;
 			case 'p':
 				if (pevent->long_size == 4)