extend JobManager TestCase

I added a testcase to the JobManagerTest to test the deferring because of missing requirements (I had problems with the JobManager in #2031). It currently fails.

If I didn't misunderstood the JobManager logic, it could be fixed by removing the `return JobResult.DEFERRED;` in the JobConsumer file.
If I put this in the run() method from the TestJob:
`Log.w("TestJob", "Iteration: " + this.getRunIteration()  + " of " + this.getRetryCount());`

The output is:
`2655-2670/org.whispersystems.jobqueue.test W/TestJob﹕ Iteration: 0 of 5`
`2655-2670/org.whispersystems.jobqueue.test W/TestJob﹕ Iteration: 0 of 5`
`2655-2670/org.whispersystems.jobqueue.test W/TestJob﹕ Iteration: 2 of 5`

With `job.setRunIteration(runIteration+1);` the output is like expected:
`2584-2600/org.whispersystems.jobqueue.test W/TestJob﹕ Iteration: 0 of 5`
`2584-2600/org.whispersystems.jobqueue.test W/TestJob﹕ Iteration: 1 of 5`
`2584-2600/org.whispersystems.jobqueue.test W/TestJob﹕ Iteration: 2 of 5`