Get a single job property uuid - Job uuid. prop - (String) property name cb - callback f(err, value)
function (uuid, prop, cb) {
            if (jobs[uuid]) {
                return cb(null, jobs[uuid][prop]);
            } else {
                return cb(new e.BackendResourceNotFoundError(sprintf(
                  'Job with uuid \'%s\' does not exist', uuid)));
            }
        }