Fix flaky DSS TO API test (sometimes CDN doesn't match)

[rawlinp]

What does this PR (Pull Request) do?

Fix this flaky TO API test:

TestDeliveryServiceServers: deliveryserviceservers_test.go:186: POST delivery service servers: 400 Bad Request[400] - Error requesting Traffic Ops https://trafficops.infra.ciab.test:443/api/2.0/deliveryserviceserver {"alerts":[{"text":"server and delivery service CDNs do not match","level":"error"}]}

• This PR is not related to any Issue

Which Traffic Control components are affected by this PR?

• TO API tests

What is the best way to verify this PR?

Run the v1/v2/v3 TO API tests, verify they pass.

The following criteria are ALL met by this PR

• This PR includes tests
• no docs necessary
• no changelog necessary
• This PR includes any and all required license headers
• This PR does not include a database migration
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[ocket8888]

Changes look good, all client/api integration tests passing