fix name check for jobs within folders

Jobs within folders (#78) is not working because the name check is checking fully qualified names and the '/' character is invalid. Updated this to check only the job name. Also extracted the full-name-parsing logic into a util so it could be tested. I was able to write a test for one of the methods but for the other I'm not clear on how to mock out Jenkins.getInstance. If you have some insight on this, please let me know.