Some fixes to Cron

[pburkholder]

Trying to address a few problems with this PR:

1. Running all the tasks in sequence without waiting for them resulting in a big spike in resource consumption, hitting quota, and the failing the last run-tasks
2. Using --wait apparently uncovers some failures that were masked when we just kicked off the task and hoped for the best
3. Using set -e would cause the later tasks not to run if there was a failure earlier.