Separate unit test from integration tests

Currently all tests are executed by maven-surefire-plugin twice in the artifact org.apache.jackrabbit.vault. Once with Jackrabbit and once with Oak.

This is useless for all Unit Tests (as they should not differ) and only makes sense for real integration tests. Therefore the integration test should instead be executed by maven-failsafe-plugin. For that they need to be renamed to be included (https://maven.apache.org/surefire/maven-failsafe-plugin/integration-test-mojo.html). Also only the ITs should be executed twice.