WFLY-4084, add a regex to command completer to deal with multiple slashes in user input

https://issues.jboss.org/browse/WFLY-4084
Handle multiple slashes in the end of command for Tab press ([domain@localhost:9990 /] /host=master// It will display content under 'master' instead of root '/' ) 
The compiled pattern should be cached, probably as a constant.