Implement a "task" noun for client v2

Add a "task" noun. This will support commands that run view/run tasks on mesos slaves. The supported verbs will include:

• run - run a specific shell command on the hosts running tasks under an aurora job.
• runtask - run a specific commandline as a one-off task in a cluster without enclosing it in a job config.
• ssh - run an SSH into the sandbox where a specific task is running.