codegen: Update to Java 8
codegen: Update to Java 8

This patch changes the POM of the code generator so that it requires
Java 8 for compiling and running, as later changes will introduce code
that will only work with Java 8.

Change-Id: I4a9491b2a858a7a224d35301ec8cf07896dad312
Signed-off-by: Juan Hernandez <59e5b8140de97cc91c3fb6c5342dce948469af8c@redhat.com>

DragonRoman/ovirt-engine-sdk,DragonRoman/ovirt-engine-sdk,DragonRoman/ovirt-engine-sdk