Add teuthology-nightly-cadence (and trigger) plus teuthology-runner

[deepssin]

This enables the nightly crons to run from a jenkins pipeline.

Here are the benefits of putting this in pipeline instead of running from crontab -

• Schedules live in Git (JJB YAML) with PR review, not only on a machine’s crontab
• Runs are visible in Jenkins: history, logs, and what triggered each build
• Less tied to one host so no dependency on a single sepia account
• Easier reruns and experiments from the UI without SSH or editing live cron.

[djgalloway]

Makes sense to me conceptually. Have you pushed the jobs manually to test in Jenkins?

[deepssin]

Makes sense to me conceptually. Have you pushed the jobs manually to test in Jenkins?

@djgalloway here is one sample log - https://jenkins.ceph.com/job/preserve-teuthology-nightly-cadence-trigger/9/console