Implement agent installation

[j-rivero]

The PR implements the installation of the Jenkins agent in the node. Mostly adapted from https://github.com/ros-infrastructure/cookbook-ros-buildfarm

[nuclearsandwich]

Some questions and non-blocking comments.

[nuclearsandwich]

Earlier versions of the swarm client would start and not exit on a connection failure.
By running the agent with a bogus or unreachable jenkins server your tests will see errors in the config that lead to startup failure. So you may want to reconsider this.

[j-rivero]

I agree with you here. What you see wrong in the code about avoiding the jenkins-agent service in the case of running test environment?

[nuclearsandwich]

The not_if here won't try to start the jenkins-agent service in test environments. But I think it should start it in all cases eve if you can't connect to the server.

Suggested change

not_if { node.chef_environment == "test" }

[j-rivero]

We can try, I think that it is going to make CI to fail since the agent connection will return an error code from provisioning making the provision to stop there. Let's see if that is correct.

[j-rivero]

Let's see if that is correct.

Failing now after applying the change.

  * service[jenkins-agent] action restart  * service[jenkins-agent] action restart
    
    ================================================================================
    Error executing action `restart` on resource 'service[jenkins-agent]'
    ================================================================================
    
    Mixlib::ShellOut::ShellCommandFailed
    ------------------------------------
    Expected process to exit with [0], but received '1'
    ---- Begin output of /usr/bin/systemctl --system restart jenkins-agent ----
    STDOUT: 
    STDERR: Job for jenkins-agent.service failed because the control process exited with error code.
    See "systemctl status jenkins-agent.service" and "journalctl -xe" for details.
    ---- End output of /usr/bin/systemctl --system restart jenkins-agent ----
    Ran /usr/bin/systemctl --system restart jenkins-agent returned 1

[j-rivero]

I'm going to revert the change to make CI happy. Ticketed in #7 in the case we find time to debug and solve it.