Make testcase classnames unique

Filenames with test results contain only the class name which makes it more
difficult to find it if the same class name is present in multiple *.py files.

packages/Python/lldbsuite/test/functionalities/step-avoids-no-debug/TestStepNoDebug.py
-class ReturnValueTestCase(TestBase):
+class StepAvoidsNoDebugTestCase(TestBase):
as ReturnValueTestCase is already present in:
packages/Python/lldbsuite/test/functionalities/return-value/TestReturnValue.py

packages/Python/lldbsuite/test/functionalities/thread/crash_during_step/TestCrashDuringStep.py
-class CreateDuringStepTestCase(TestBase):
+class CrashDuringStepTestCase(TestBase):
as CreateDuringStepTestCase is already present in:
packages/Python/lldbsuite/test/functionalities/thread/create_during_step/TestCreateDuringStep.py

packages/Python/lldbsuite/test/functionalities/thread/step_until/TestStepUntil.py
-class TestCStepping(TestBase):
+class StepUntilTestCase(TestBase):
as TestCStepping is already present in:
packages/Python/lldbsuite/test/lang/c/stepping/TestStepAndBreakpoints.py

llvm-svn: 335431