It's nice to have a jenkins recipe with some of the common plugins
Uses plugins defined in attributes and uses more standard chef commands to setup Jenkins.
Splits out creation of jenkins directories rather than using the
recursive option due to permissions problems.

Adds ssh-agent plugin to default list of plugins (required for
git-client).
Merge pull request #114 from mjstallard/jenkins-recipe

It's nice to have a jenkins recipe with some of the common plugins