When you start engine (backend) after a dev install, it's already listening for remote debug connections on 8787:
ovirt-engine[8879] INFO _detectJBossVersion:187 Detecting JBoss version. Running: /usr/lib/jvm/jre/bin/java ['ovirt-engine-version',
<snip>
Listening for transport dt_socket at address: 8787
So, just do a remote debug session using your favorite IDE. I use Eclipse:
From Eclipse, Run > Debug Configurations, Remote Java, New (use the project you want to debug)
Change the port to 8787, and Debug.
Window > Perspective > Open > Debug and you can see you are now attached.