cron: Fix parsing issue with spaces
Fixes a parsing issue with older CronJobs which pre-date the current parser and normalizer system.
Also exposes a better error message if there are similar issues. That's not currently exposed to users, but I think that would require a patch to the jobs-cli instead of this repository.
Change-Id: I7431bc49fc1e4939f8bb3dfe943c81f7bb1ed1df