trace: include filename when printing parser error messages

Improves error messages from:

  ValueError: Error on line 72: need more than 1 value to unpack

To

  ValueError: Error at /home/berrange/src/virt/qemu/trace-events:72:
    need more than 1 value to unpack

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180306154650.24075-1-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/scripts/tracetool.py b/scripts/tracetool.py
index c55a215..fe2b077 100755
--- a/scripts/tracetool.py
+++ b/scripts/tracetool.py
@@ -142,7 +142,7 @@
     events = []
     for arg in args:
         with open(arg, "r") as fh:
-            events.extend(tracetool.read_events(fh))
+            events.extend(tracetool.read_events(fh, arg))
 
     try:
         tracetool.generate(events, arg_group, arg_format, arg_backends,