Fix bug where JobStatusCommand can throw NPE

This could happen when getting host status. We first get a list of all
jobs, then the status for each job. If a job was deleted between those
two steps, we would throw a NPE when trying to process its status.

-RN
Fixed bug where 'helios status --host' would sometimes throw NPE
Merge pull request #266 from spotify/rculbertson/host-status-fix

Fix bug where JobStatusCommand can throw NPE