What changes are you introducing?

Reduce number of "ifeval" macros.

Why are you introducing these changes? (Explanation, links to references, issues, etc.)

It is easier to look at the macro than finding out what the value of "client-os" is for certain builds or assemblies.

Anything else to add? (Considerations, potential downsides, alternative solutions you have explored, etc.)

Contributor checklists

• I am okay with my commits getting squashed when you merge this PR.
• I am familiar with the contributing guidelines.

Please cherry-pick my commits into:

• Foreman 3.19/Katello 4.21
• Foreman 3.18/Katello 4.20 (Satellite 6.19; orcharhino 7.9)
• Foreman 3.17/Katello 4.19
• Foreman 3.16/Katello 4.18 (Satellite 6.18; orcharhino 7.6, 7.7, and 7.8)
• Foreman 3.15/Katello 4.17
• Foreman 3.14/Katello 4.16 (Satellite 6.17; orcharhino 7.4; orcharhino 7.5)
• We do not accept PRs for Foreman older than 3.14.