[Core] Introduce class-based scenarios

This adds support of scenarios implemented as classes
in addition to existing method-based scenarios.

First class-based scenario will be added in next patch.

Implements: class-based-scenarios
Change-Id: Ia383226a356cf1b24ac7125c028f547d9de74c0d

tests/unit/fakes.py

@@ -1662,6 +1662,14 @@ class FakeScenario(scenario.Scenario):
         raise multiprocessing.TimeoutError()
 
 
+@scenario.configure(name="classbased.fooscenario")
+class FakeClassBasedScenario(FakeScenario):
+    """Fake class-based scenario."""
+
+    def run(self, *args, **kwargs):
+        pass
+
+
 class FakeTimer(rally_utils.Timer):
 
     def duration(self):

tests/unit/test.py

@@ -200,9 +200,6 @@ class FakeClientsScenarioTestCase(ScenarioTestCase):
         self._fake_clients = fakes.FakeClients()
 
 
-def get_test_context():
-    return {
-        "task": {
-            "uuid": str(uuid.uuid4())
-        }
-    }
+def get_test_context(**kwargs):
+    kwargs["task"] = {"uuid": str(uuid.uuid4())}
+    return kwargs