Omnibus (embedded) fails the 'users' cookbook's need for ruby-shadow

When using the embedded chef-full package, installing a system-level ruby package has no impact.

This is evidenced by using the "users" cookbook, with adaptation to create passwords.

The system has libruby-shadow1.8 installed, but this is not found by the embedded ruby.

Since the cookbook is using a platform determination to decide what package to install, it probably should determine if it is running under omnibus/embedded, and thereby install the gem via gem_package instead.