Cleanup of jenkins init scripts run on EC2 VMs

- Add SSH known_hosts for gerrit instances
- Don't run apt-get update as jenkins doesn't run as root or have
  sudo rights to add/update packages.
- Cleanup and commenting of what each section does

Change-Id: I89571bb988a211b226c0b8568b3c1f8ad7226340
diff --git a/jenkins-scripts/create_jenkins_user.sh b/jenkins-scripts/create_jenkins_user.sh
index 86a5c92..becdfd6 100755
--- a/jenkins-scripts/create_jenkins_user.sh
+++ b/jenkins-scripts/create_jenkins_user.sh
@@ -34,8 +34,8 @@
 fi
 
 mkdir /home/jenkins/.ssh
-mkdir /w
 cp -r /home/${OS}/.ssh/authorized_keys /home/jenkins/.ssh/authorized_keys
+
 # Generate ssh key for use by Robot jobs
 echo -e 'y\n' | ssh-keygen -N "" -f /home/jenkins/.ssh/id_rsa -t rsa
 chown -R jenkins:jenkins /home/jenkins/.ssh /w