[keycloak-dev] Enable JDK8 for testsuite

I've changed source/target to 1.8 for testsuite/integration-arquillian. This is so I can use lambdas for testing permissions (otherwise I end up with extremely messy tests with loads of anonymous inner classes). Anyone have any issues with that? In 2.x we can look at setting 1.8 as default for everything except adapters and shared modules.