Jenkins security change

I've made a change to Jenkins' configuration in response to a security
advisory[1], which restricts slave/master communications.

If any jobs that usually pass begin to fail with SecurityException
errors, please let me know and I can check if it's caused by this config
change.

[1]https://wiki.jenkins-ci.org/display/SECURITY/Jenkins+Security+Advisory+2014-10-30

··· -- Dominic Cleal Red Hat Engineering