Hostnames in dev environment fail validator, makes no-op PATCH error

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API

SUMMARY

A new Instance hostname validator fails with the basic docker development environment.

Also, we seem to validate the field even when it's not changing, which makes it hard to do other things in the API.

ENVIRONMENT

• AWX install method: developer environment

STEPS TO REPRODUCE

Start the docker-compose development environment with 1 hybrid instance.

PATCH with default data

https://localhost:8043/api/v2/instances/1/

EXPECTED RESULTS

A 200 response code.

ACTUAL RESULTS

A 400 response code with

{
    "hostname": [
        "illegal characters detected in hostname=awx_1. Please verify."
    ]
}

ADDITIONAL INFORMATION

It seems questionable that we allow registration with a hostname that would fail validation?

Provided that we don't want to fix that, then we must assume that we have invalid hostnames in all cases, and it would be nice to only validate when it is changing.