[8.x] WFLY-794: adds missing package in sun.jdk module, adds simple test to en...

...sure rmi context is in jndi, and enhances the existent jmx connector test to run remotely

Related PR for master: #6428
I did a few things to simplify the test, that was to remove the deployment's manifest (which was needed due to xnio dependency). Is that really needed?