verify installation works before sending ER/RC emails

As seen in CRW-4107, it's possible to release an RC but forget to push it to stage.

Here's a proposed enhancement to the current https://main-jenkins-csb-crwqe.apps.ocp-c1.prod.psi.redhat.com/job/DS_CI/job/Releng/job/send-email-qe-build-list_3.x and https://main-jenkins-csb-crwqe.apps.ocp-c1.prod.psi.redhat.com/job/DS_CI/job/Releng/job/send-email-qe-build-list_3.5 jobs.

1. We need:

• for an ER – install the ER bits from brew.reg
• for an RC – default to installing the RC bits from brew.reg, but with boolean flag to instead installFromStaging if the bits have been staged in errata; this will fail to send the email if there's a mismatch in versions or the install job fails
• And as to version to install, it would be from latest (not prev or next) on 4.10 or 4.12 (not sure which is better as we support both but want to encourage customers to move up)

Dmytro says this job can take up to 20 mins to run, and based on recent data it appears to take 10-15 mins for PSI and AWS installs.

2. Add a note on the build page reminding the sender to make sure they've staged the bits in errata (if applicable, for RCs close to the end of the release cycle).

3. Even better than a note, could we use the errata API to trigger a push to stage as part of this email?

Then the job would:

• trigger errata move to QE state
• trigger errata push to stage
• collect list of images in brew.reg that we want to see in reg.stage
• wait until complete (watching for UMB notification? polling stage registry for latest images at intervals of 5 mins?
• once stage push is done, verify images in stage == images in brew.registry
• trigger install job above