WFLY-3881 User shouldn't be able to use empty JDNI name ('java:/' or 'java:jboss/')

https://issues.jboss.org/browse/WFLY-3881
https://bugzilla.redhat.com/show_bug.cgi?id=1019260

Tested.
David, Thank for review.
This PR is for fixing BZ1019260, I think it is reasonable and could fix quickly.

Your suggest is correct, we need to do more validation to make JNDI name is correct.