Show results of last task without requring user to lookup UUID

Currently to view the results of the last task/benchmark a user must
list tasks, copy a UUID, then query for that UUID. This commit alows the
user to specify 'last' instead of a UUID to retrieve the results of the
last task.

Change-Id: I8ffe1bb8d925a6a114e4dd12be2f1af13e1bfced