Use the server built in Infinispan even if INFINISPAN_TEST_SERVER_DIR is null in ContainerInfinispanServerDriver

We would like to standardize the test suite. It means that all modules should be tested with the same arguments when the mvn verify command is executed.

The idea is to use the server built in Infinispan even if INFINISPAN_TEST_SERVER_DIR is null in ContainerInfinispanServerDriver.

External projects that are using the Infinispan JUnit modules won't be impacted because they are not building the Infinispan Server locally.