Fix t3c non-topo edge-origin DS params

[rob05c]

Fixes cache config generation for non-topology DSes that are edge->origin (via the edge's cachegroup's parent being the origin cachegroup) for DS Parameters.

Due to a bug in the non-topology logic to determine if a cache is the last cache tier, that scenario was resulting in the config gen thinking the edge wasn't the last tier, and not inserting MSO retry parameters on the parent line.

Fixing that bug exposed another bug, in the unavailableServerRetryResponsesValid regex. I changed that function to simply call ParseRetryResponses and return whether there was an error. Actually parsing is probably faster than the regex anyway, and this is the safest way to prevent bugs and discrepancies in the parse vs can-parse functions.

This also fixes several tests around both of those bugs, which were testing the wrong things. It fixes both the retry parameter tests, which were accidentally testing that the last tier had the first tier params, and a remap.config test that was testing edge->origin http/https rewriting as if it were edge->mid.

Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Control Cache Config (t3c, formerly ORT)
• Traffic Control Health Client (tc-health-client)
• Traffic Control Client
• Traffic Monitor
• Traffic Ops
• Traffic Portal
• Traffic Router
• Traffic Stats
• Grove
• CDN in a Box
• Automation
• unknown

What is the best way to verify this PR?

Run tests. Generate config for a non-topology DS which is edge->origin and has DS retry parameters, verify retry parameters are inserted into parent.config correctly.

If this is a bugfix, which Traffic Control versions contained the bug?

• 6.0.0 and newer

PR submission checklist

• This PR has tests
• [x] This PR has documentation no docs, no interface change
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[traeak]

Fixes look okay, make sense and testing on prod data shows the fix works.