adding tunneling option for JNLP slave agents. This came from Ken Hofsass who...

adding tunneling option for JNLP slave agents. This came from Ken Hofsass who needed the connection to the server be tunneled for security reasaons.

jnlp-agent needs to be updated to take this into account.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@11638 71c3de6d-444a-0410-be80-ed276b4c234a