fix multi-parent hooks to wok with --local-checkout-dir

[jtnord]

improves multi-parent hooks to work with a local checkout when testing a single plugin

tested with the aws-java-sdk-minimal plugin in a local checkout.

--working-dir=c:\workarea\source\github\cloudbees\unified-release\output-oc-it\work
--war=c:\workarea\source\github\cloudbees\unified-release\products\core-cm\target\core-cm.war
--fallback-github-organization=jenkinsci-cert
--external-hooks-jars=c:\workarea\source\github\cloudbees\unified-release\tests\cb-pct-hooks\target\cb-pct-hooks.jar
--include-plugins=oc-it
--local-checkout-dir=c:\workarea\source\github\cloudbees\unified-release\.\tests\operations-center-it
-Dsurefire.excludesFile=c:\workarea\source\github\cloudbees\unified-release/src/test/resources/pct-surefire-exclusion-list
-Dsurefire.rerunFailingTestsCount=0
-DreuseForks=false
-DforkCount=1
-Dmaven.test.failure.ignore=true

needs further testing

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[jtnord]

this was broken as the plugin name would be set to the artifactId of the root of the checkout which for multimodule projects is always wrong.

as we are only testing a single pluign we know the name which is the artifactId so use it.

[jtnord]

mostly obsolete by #510 , some work is still required but to do in a different PR