oeqa/selftest/case: Migrate case class to the new OEQA framework
Summary of the changes:
- Use OETestCase as base class instead of unittest.TestCase
- Remove LogResults decorator the new framework provides logging into
the core functionality.
- Logger is now self.logger instead of self.log
- Move comments into docstrings in several help methods
- Use get_test_layer() method instead of access monkey patched variable
in old oeSelfTest case class.
