Explicitly call the planner with Python

This is to force the planner to be executed with the configuration-
specified Python version and not the default one.

benchmark.py

@@ -183,6 +183,7 @@ def runJob(configuration, instance, config):
 		config["executables"]["timeout"]["binary"],
 		"-m=" + str(config["limits"]["memory"]),
 		"-t=" + str(config["limits"]["time"]),
+		config["executables"]["python"]["binary"],
 		config["executables"]["planner"]["binary"],
 		"--domain=" + inputFiles["domainFile"],
 		inputFiles["instanceFile"],