Improve ITs for set goal

[slawekjaranowski]

We have about 37 - versions-maven-plugin/src/it/it-set-* integrations test for set goal ...
but looks like not cover every cases.

Before working on issue like: #1103 will be appreciated to refresh a little those.

Task to do:

• add a url with link to source issue as possible to discover
• drop invoker.nonRecursive from invoker.properties as set goal is aggregate already
• drop not used pluginManagement from poms
• rewrite verify scripts
  • change to groovy
  • use XmlSlurper for verifying
  • check all items in all modules - what are changed - can be done be diff eg on: target/it/it-set-001/pom.xml target/it/it-set-001/pom.xml.versionsBackup

Step for quick checks:

• mvn install - need only once
• mvn verify -DskipTests -pl versions-maven-plugin -P run-its -Dinvoker.test=it-set-\*

Can be done one by one.