(21868) Move puppet libary target to /Library/Ruby/Site

We currently drop the puppet library files in /usr/lib/ruby/site_ruby/1.8 on
OSX, which is a symlink to /Library/Ruby/Site/1.8. As of OSX 10.9 Mavericks,
this will no longer work because it will be ruby 2.0.0. There are hard ways
and easy ways to solve this problem. A hard way would be to somehow
introspect the target host at install time, and then dynamically copy the
payload into the correct ruby version specific path. Another hard way would
be to create different OSX packages for different versions of OSX. Or, we
could pick the easy way, which is to just install into /Library/Ruby/Site
(the equivalent of /usr/lib/ruby/site_ruby). Since puppet will work on all
rubies shipped with supported versions of OSX, this will "just work".

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>