Update test server config

[ricellis]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [x] Added tests for code changes or test/build only changes
• [x] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

Change the test server configuration and allow for overriding the token server used by tests.

1. Steps to reproduce and the simplest code sample possible to demonstrate the issue

Run Jenkins tests

2. What you expected to happen

Tests to pass

3. What actually happened

Tests failed because of a server config problem.

Approach

Replace the test server configuration in Jenkinsfile.

Schema & API Changes

• "No change"

Security and Privacy

• "No change"

Testing

• Modified existing IAM auth plugin tests to use configured IAM token server when not nocked.

Monitoring and Logging

• "No change"