Improve logging with assertions

[gingerwizard]

Currently logging with assertions only indicates the task name failing. In the case of composite operations this makes it quite hard to identify which query actually failed the assertion.

I think this is small change on the Asserting Runner e.g.

    async def __call__(self, *args):
        params = args[1]
        return_value = await self.delegate(*args)
        if AssertingRunner.assertions_enabled and "assertions" in params:
            if isinstance(return_value, dict):
                for assertion in params["assertions"]:
                    try:
                        self.check_assertion(assertion, return_value)
                    except exceptions.RallyTaskAssertionError as e:
                        self.logger.info(f"Assertion failed on: {[params.get('name')]}")
                        raise e
            else:
                self.logger.debug("Skipping assertion check as [%s] does not return a dict.", repr(self.delegate))
        return return_value

The AssertingRunner has no visibility of the child runner and we dont have any guarantee of the params in args. The name should exist however and would be sufficient if the user names their searches uniquely within a composite - which should be good practice.