Update Astrolabe workload executor to utilize the driver's unified test runner for executing the workload.

Notes:

• In languages that don't ship the Unified Test Runner as part of their distribution, a solution will need to be identified in order to use the runner in Astrolabe.
• The runner needs to be passed arguments, like the URI, from Astrolabe via the workload executor, so changes may be needed in the executor or the runner, and possibly both.