Add time zone support to chef-jenkins

I have made changes to chef-jenkins to support the addition of a time zone attribute (node.jenkins.time_zone). This allows you to configure the jenkins time zone via chef.

In the process, of working this issue, I also discovered that if you restart a chef-jenkins install of jenkins using the service command, that a different config file (/etc/sysconfig/jenkins) vs. the config file created by chef-jenkins.

To address this issue, I have modified jenkins::default to remove the config file at /etc/sysconfig/jenkins and link it to /etc/default/jenkins.

I believe these are positive additions to chef-jenkins. Hopefully, you will accept them.