Fixes: Maven2 builds with non-standard test mojos failed.

Not observed in actual usage, but reproducible (for me at least, though apparently not ci.jenkins-ci.org) in a test:
java.lang.AssertionError: null
    at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:628)
    at jenkins.model.lazy.AbstractLazyLoadRunMap.all(AbstractLazyLoadRunMap.java:581)
    at jenkins.model.lazy.AbstractLazyLoadRunMap.entrySet(AbstractLazyLoadRunMap.java:243)
    at java.util.AbstractMap$2$1.<init>(AbstractMap.java:378)
    at java.util.AbstractMap$2.iterator(AbstractMap.java:377)
    at hudson.util.RunList.iterator(RunList.java:103)
    at hudson.util.RunList.size(RunList.java:114)
    at hudson.maven.MavenProjectTest.testDeleteSetBuildDeletesModuleBuilds(MavenProjectTest.java:159)

to determine which test result files belong to the mojo execution

[FIXED JENKINS-8334] use heuristics to detect test-mojos instead of relying on hard-coded plugin names

After all, that's the installation the user is most likely going to choose, and if there's only one installation.

Plus when there's only one installation, there's no drop-down to select the Maven installation in the config UI, so the user is asked to do a rather unnatural "open config page" > "just click save" workflow.

It breaks some already fixed issues like JENKINS-1557

of project with maven-failsafe-plugin

Do not inject testFailureIgnore to
maven-failsafe-plugin:integration-test because it doesn't exist and
causes an NPE with Maven2.
Only insert it for maven-failsafe-plugin:verify.

(cherry picked from commit bdad2a3d)

maven-failsafe-plugin deserves the same level of integration
as maven-surefire-plugin.

A failed IT should mark the build as unstable, not failed.