fix test return value

validation/mbtests.py

 import unittest
+import sys
 all_tests = [
         "poiseuille.poiseuille",
         "cavity.cavity",
@@ -6,6 +7,8 @@ all_tests = [
 suite = unittest.TestSuite()
 for t in all_tests :
     suite.addTest(unittest.defaultTestLoader.loadTestsFromName(t))
-unittest.TextTestRunner().run(suite)
+r = unittest.TextTestRunner().run(suite)
+print(r)
+sys.exit(r.wasSuccessful())