Make Jenkins::Plugin resources idempotent

Without this patch Puppet configuration are not idempotent when
configuring Jenkins.

This patch addresses the problem by checking if the plugin file has
already been downloaded in an idempotent way.
Bind Jenkins to LDAP

Without this patch jenkins has no authentication.  This is a problem
because we're not really demonstrating a distributed system.  This patch
addresses the problem by binding jenkins to LDAP for user
authentication.  With this patch applied Jenkins is configured to lookup
user accounts in LDAP and the user "jeff" with password "Password1" will
work to log in to the jenkins service.
Update packages to unclude ruby-devel

Without this patch the puppet spec job doesn't work because gem native
extensions cannot be compiled without the ruby header files in place on
the system.  This patch addresses the problem by installing the ruby
header files located in the ruby-devel package.
Add sqlite-devel package for puppet gem dependencies
Add rubygem-rdoc package for puppet gem dependencies