workaround odd nose problem causing the run_tests function to be called even if the file is not main - refs #1539

tests/python_tests/utilities.py

@@ -58,8 +58,9 @@ def get_unique_colors(im):
     pixels = sorted(pixels)
     return map(pixel2rgba,pixels)
 
-def run_tests(iterable):
+def run_tests(iterable=None):
     failed = 0
+    if iterable:
         for test in iterable:
             try:
                 test()