Support testing with multiple Maven versions

[kwin]

Often ITs for Mojos should be tested against multiple Maven versions. To ease parametrisation (e.g. in a CI/CD environment) the list should not be hardcoded into different maven-failsafe-plugin executions but rather be given with a dedicated System property like "it.mavenHomePaths" which should support multiple comma-separated paths.
All unit test method should then be executed against all of the given Maven versions.