Aggregate junit results at parent test level

Currently, we only aggregate child TAP at the parent test build level.


It would be nice if we could do the same for JUnit test results (i.e., openjdk tests).
- JUnit result at the child job level: https://openj9-jenkins.osuosl.org/job/Test_openjdk17_j9_sanity.openjdk_aarch64_linux_OMR_testList_1/252/testReport/

- https://github.com/adoptium/aqa-tests/blob/master/buildenv/jenkins/JenkinsfileBase#L985

That is, we can see the aggregated child job JUnit results at the parent build level.

Start at buildenv/jenkins/JenkinsfileBase around line 985 and compare the existing child TAP aggregation with the child JUnit report linked in the issue. Confirm how the parent build currently exposes child results, then make the parent build show aggregated JUnit results for the child jobs. Done means the parent-level report includes the child JUnit results, such as those from the linked OpenJDK test job.

Written by the indexing model from the issue text.