WIP: Supporting multiple hostnames for Atmosphere(1) server

[c-mart]

Description

Allows an atmosphere(1) server to answer on multiple hostnames so that we can do rolling deployments to a fresh instance and fast cutovers during a short maintenance period.

Co-depends on clank #257.

Checklist before merging Pull Requests

• New test(s) included to reproduce the bug/verify the feature
• Add an entry in the changelog
• Documentation created/updated (include links)
• If creating/modifying DB models which will contain secrets or sensitive information, PR to clank updating sanitation queries in roles/sanitary-sql-access/templates/sanitize-dump.sh.j2
• Reviewed and approved by at least one other contributor.
• New variables supported in Clank
• New variables committed to secrets repos

[coveralls]

Coverage increased (+0.008%) to 37.346% when pulling 7ef60ac on c-mart:multiple-hostname-support into 4daba78 on cyverse:v32.

[coveralls]

Coverage increased (+0.008%) to 37.346% when pulling 7ef60ac on c-mart:multiple-hostname-support into 4daba78 on cyverse:v32.