Adjust IPI 4.15 job schedules and disable PowerVS 4.14 UPI jobs

[Poorna-Gottimukkula1]

• Adjusting ipi jobs schedule's as madrid and frankfurt running concurrently as a results they're conflicting with each other on image pulls apparently.
• Disable 4.14 PowerVS UPI job.
• Reduced the build-discarder num-to-keep to 30
• disable jenkins-backup job

[ppc64le-cloud-bot]

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