doc: fix python example

Problem: A job submission Python example in the docs has an error,
so it won't run, making it a poor example. It also prints the raw
JobInfo object, which isn't very demonstrative.

Update the example to fix the error and print something useful from
the returned JobInfo result object.

Author: grondo

doc/python/job_submission.rst

@@ -216,13 +216,15 @@ as futures complete.
 		result_fut.then(result_cb)
 
 	def result_cb(fut):
-		print(fut.get_info())
+		job = fut.get_info()
+		result = job.result.lower()
+		print(f"{job.id}: {result} with returncode {job.returncode}")
 
 	flux_handle = flux.Flux()
 	jobspec = flux.job.JobspecV1.from_command(["/bin/true"])
 	for _ in range(5):
 		# submit 5 futures and attach callbacks to each one
-		submit_future = flux.job.submit_async(f, jobspec)
+		submit_future = flux.job.submit_async(flux_handle, jobspec)
 		submit_future.then(submit_cb, flux_handle)
 	# enter the flux event loop (the 'reactor') to trigger the callbacks
 	# once the futures complete