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/director_unroll_runme.py

@@ -16,5 +16,4 @@ c = b.get()
 
 
 if not (a.this == c.this):
-    print a, c
-    raise RuntimeError
+    raise RuntimeError("{} {}".format(a, c))