JobRunner should support kill and status commands.

The JobRunner is the central place to launch Samza jobs. We use run-job.sh to invoke the JobRunner, which then launches the job as described here:
http://samza.apache.org/learn/documentation/0.11/jobs/job-runner.html

Note that the JobRunner works for any job that implements the StreamJob interface, so it works with YarnJob, ProcessJob, and so on.

However, to kill or get the status for a job, we only have a set of YARN-specific scripts.

Since the StreamJobs all implement the kill() and getStatus() methods, there's no reason we can't similarly leverage the StreamJob abstraction to perform these operations as well.

The proposal is to update JobRunner to support all 3 commands.

The benefits are:
1. A common abstract way to start, stop, and get status for any type of StreamJob.
2. For features like multistage (samza-1041), this will be a much easier way to collectively manage a set of processors as separate (e.g. YARN) applications