Remove print statements from Python tests

Use exceptions instead of printing to stdout.
Part of an effort to convert Python tests to python 3 syntax.

Examples/test-suite/python/li_std_wstream_runme.py

@@ -8,5 +8,4 @@ o = wostringstream()
 o << a << u" " << 2345 << u" " << 1.435 << wends
 
 if o.str() != "A class 2345 1.435\0":
-    print "\"%s\"" % (o.str(),)
-    raise RuntimeError
+    raise RuntimeError("str failed: \"%s\"".format(o.str()))