scripts/tracetool: don't barf on formats with precision

This only affects lttng user space tracing at the moment.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/__init__.py

@@ -228,7 +228,7 @@ class Event(object):
                                           self.args,
                                           fmt)
 
-    _FMT = re.compile("(%\w+|%.*PRI\S+)")
+    _FMT = re.compile("(%[\d\.]*\w+|%.*PRI\S+)")
 
     def formats(self):
         """List of argument print formats."""