external tests workflow does not work with ITERATIONS

In ITERATIONS, we repeatedly run the same test n times. It looks like the external test workflow does not work with ITERATIONS. At the end of each test, we do clean - `docker rmi`
https://github.com/adoptium/aqa-tests/blob/1236ede6168d38482806ab89a8b3a298fccbdf80/external/spring/playlist.xml#L26
https://github.com/adoptium/aqa-tests/blob/1236ede6168d38482806ab89a8b3a298fccbdf80/external/external.sh#L203

This will result in the subsequent test failure due to missing the image.

```
16:34:20 docker run -v /home/jenkins/workspace/Grinder_iteration_4/openjdkbinary/j2sdk-image:/opt/java/openjdk --rm adoptopenjdk-spring-test:11-jdk-ubuntu-openj9-full
16:34:20 Unable to find image 'adoptopenjdk-spring-test:11-jdk-ubuntu-openj9-full' locally
16:34:22 docker: Error response from daemon: pull access denied for adoptopenjdk-spring-test, repository does not exist or may require 'docker login': denied: requested access to the resource is denied.
16:34:22 See 'docker run --help'.
16:34:22
16:34:22 spring_test_0_FAILED
```

Start with external/spring/playlist.xml at line 26 and external/external.sh at line 203, then reproduce the workflow with ITERATIONS enabled. Trace the docker rmi cleanup between iterations and verify that the next iteration can run the required image; done means repeated external tests complete without the missing-image failure.

Written by the indexing model from the issue text.