trace.py: fix failure on newest Python

After https://www.python.org/dev/peps/pep-0479/ was done in Python 3.5
four years ago, it appears that recently Python 2.7.15 on Fedora 29 (at
least that's what I tested) suddenly implemented this change as well.

This change means that a generator cannot call just call next() on some
iterator hoping that the end of iteration (via StopIteration exception)
will automatically translate to an end of the generator. We now need to
do this manually.

Before this patch, "make check" fails on my Fedora 29, with the
smoke_tracing_test part failing when it runs trace.py.

Signed-off-by: Nadav Har'El <[email protected]>

scripts/osv/trace.py

@@ -166,7 +166,10 @@ def align_up(v, pagesize):
 def do_split_format(format_str):
     chars = iter(format_str)
     while True:
-        c = next(chars)
+        try:
+            c = next(chars)
+        except StopIteration:
+            return
         if c in '<>=!@':
             raise Exception('Not supported: ' + c)
         if c == '*':