only declare which Ruby we need once
only declare which Ruby we need once

This looks weird, but makes it so we only have to change what Ruby the
package depends on once.

Also, should use $(pkg_path_for ..) function in plans, not a shell out
to the $(hab pkg path ..) command.

Signed-off-by: Robb Kidd <a629c362624370ec351e141df0bd1d27621ff790@thekidds.org>

chef/chef-dk,chef/chef-dk,chef/chef-dk