refs #9906. unit test to system test.

Convert unit tests into system tests, but also update the stresstesting base class
to derive from unittest TestCase to remove the need for customised assert methods.
refs #9906. Python 2.6 limitation.

assertGreater, assertLess not supported until 2.7. Also forgot to add module.
Merge remote-tracking branch 'origin/feature/9906_RRO_auto_unit_test'