Fixing Rally config json schema

The patch extends the json schema used to validate the input Rally config.
New keys have been added according to recent changes in the test engine
(see benchmark.rally.utils.ScenarioRunner.run() method).

Blueprint test-engine
Closes-Bug: #1237285
Change-Id: I98d5add2b7b11c5c46abe9eca57bc70eeb11e955
Merge "Fixing Rally config json schema"