[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
IIRC we discussed that in IRC, I suspect it was something left behind when doing the old test, anyway it's not needed or useful in the "new" test