Clarify how to launch the Jenkins Docker PBS node

[tfnico]

I just got the plugin up and running using the docker-based PBS server, but had some issues on the way:

• The docker container does not expose port 9618, and I think leaving this out lead to a PBS Status panel without any queues in it.
• The documentation does not clearly state that the Jenkins slave should run inside the docker container (if I understand it correctly). For this you first need to manually install Java inside the container in order to launch the slave process (I saw some failing automatic Java install). yum install java-1.8.0-openjdk.x86_64 inside the container was easier.
• The container does not expose its own SSH connection where Jenkins can connect, nor does the documentation say to configure a different port than that of the docker host.
• The documentation does not say which credentials to use for launching the slave in the container. I used the root/root login that ships with the image.

So I roughly ended up with these steps in order to get it working:

docker run -it -h pbs.local -p 10022:22 -p 9618:9618 --privileged agaveapi/torque bash
# the above command will start an interactive shell in the container.
yum install java-1.8.0-openjdk.x86_64 # in order to launch slave
/usr/bin/supervisord # starts pbs server, and sshd
# now create the slave in jenkins with SSH port 10022 and credentials root/root 

[kinow]

I hope you don't mind if I shamelessly steal your steps and update the docs in the next days. Or if you have spare time and can submit a pull request (to pbs-plugin's README, as a Wiki page, or even to biouno.github.io) I'll give it a try and merge it.

Thanks @tfnico !